Abstract:
A hybrid speed and or proximity sensor may include a variable reluctance sensor with an added excitation circuit. Similarly, a hybrid speed and or proximity sensor may include a variable inductance proximity sensor having a magnet and a magnetically permeable pole piece added in the sensor. It is emphasized that this abstract is provided to comply with the rules requiring an abstract, which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The present invention relates generally to the field of inductive sensors and more particularly to hybrid inductive speed and proximity sensors that measure speeds approaching zero.  
         [0003]     2. Background Information  
         [0004]     Rotary and linear inductive sensors, such as the variable reluctance speed sensor (VRSS) as shown in  FIG. 1 , or variable inductance proximity sensors as shown in  FIG. 2  or induction sensors using permanent magnets on the target as shown in  FIG. 3 , have many years of reliable service. However, conventional, manned flight approved sensors can not accurately measure speeds approaching zero and have difficulty measuring the speed of targets without surface irregularities and also require close proximity between the sensor and the target. Variable reluctance speed sensors and induction sensors, either rotary or linear, require movement of a scrutinized target to generate a signal used to monitor speed. Accordingly, there is a target speed below which variable reluctance or induction speed sensors may not be useful.  
         [0005]     Many variable inductance sensors may not have a permeable pole piece. This has consequences when using the typical variable inductance sensor with an induction-style permanent magnet on the target. Many variable inductance sensors that incorporate external AC excitation often require the sensor to be within approximately {fraction (1/2)} of a coil diameter of the target that is being monitored to accurately measure speed or proximity. Assuming the permanent magnet is too far away to be influenced by the high frequency field coming from the sensor, the magnetic field from a permanent magnet on the rotating target may have no influence on a variable inductance sensor without a permeable pole piece. Thus, a magnet on the rotating target may be of no help in facilitating the use of the typical variable inductance sensor for zero-speed or proximity measurement across relatively large gaps or through significantly thick or dense conductive material. Sensors having a ferromagnetic or diamagnetic pole piece may be needed to sense the field from the permanent magnet.  
         [0006]     What is needed is a zero speed sensor and or proximity sensor having proven manned flight safety and reliability.  
       SUMMARY OF THE INVENTION  
       [0007]     A hybrid speed and or proximity sensor may include a variable reluctance sensor with an added excitation apparatus. Similarly, a hybrid speed and or proximity sensor may include a variable inductance proximity sensor with an added permanent magnet in or on the target or an added permanent magnet and magnetically permeable pole piece in the sensor.  
         [0008]     A variable reluctance sensor with an excitation apparatus added to the sensor coil benefits from the tried and tested reliability of a variable reluctance sensor while introducing the accurate low speed measurement of a variable inductance sensor. If the variable inductance circuit fails, the variable reluctance speed sensor remains capable of accurately functioning. Therefore, the capabilities of a variable inductance sensor can be incorporated without the risks associated with a device that has no history of manned space flight use.  
         [0009]     Additional benefits of a hybrid sensor include, a signal at speeds approaching zero, a usable signal from smooth targets, greater detection range through metal housings and over moderate gaps and signal amplitude that is not speed dependent. In the case of a hybrid sensor that incorporates a magnet on the target, this extends the additional benefits beyond moderate gaps to large gaps.  
         [0010]     A hybrid sensor according to the present disclosure may reduce or eliminate the cost and schedule impact associated with between-flight Space Shuttle Main Engine (SSME) removal and torque checks. Between-flight torque checks of the SSME pumps may impose a cost of 50 to 100 man-hours per flight. The SSME heat shields must be removed prior to performing the torque checks on its pumps. Heat shield removal is one of several other torque-check associated costs. Additionally, if heat shields can be left on between flights, this is one step toward leaving the engines in the space shuttle between flights generating the potential for further indirect savings. A hybrid sensor may realize at least 50 to 100 man-hours savings in turnaround time per flight and in the best scenario it may facilitate turnaround of the space shuttle without SSME removal. This would lead to a reduction in parts and processes associated with engine removal such as seals, fasteners, soap solution, tools, and paperwork. Also, the incorporation of the hybrid sensor technology will allow detection of an anomalous run torque within 2 hours after Main Engine Cutoff (MECO). Therefore, even if the between-flight SSME removal and torque checks are not eliminated, pump diagnosis and maintenance strategy can occur long before the shuttle returns to the ground. If the in-flight run torque proves trustworthy, there may be a reduction in orbiter processing and cycle time.  
         [0011]     Z-speed is a colloquial term referring to a family of tools and techniques, which measure the speed of a target at or near zero speed. It originally meant literally zero speed, but as the tools and techniques have evolved, it has taken on a less precise meaning. The target can be rotating and/or translocating.  
         [0012]     Excitation apparatus may be added to existing variable reluctance sensor designs without destroying the ability of the variable reluctance sensor to function as a variable reluctance sensor. Accordingly, the zero speed function associated with the variable inductance sensor can be obtained without compromising the reliability of the variable reluctance sensor. If the zero speed measurement circuit fails, the traditional variable reluctance function would still be present. This redundancy amounts to a significant reward with an insignificant risk.  
         [0013]     Accordingly, the proximity sensing function associated with the variable inductance sensor can be obtained without compromising the reliability of the variable reluctance sensor. If the proximity sensing circuit fails, the traditional variable reluctance function would still be present. Again, this amounts to a significant gain without a significant risk.  
         [0014]     In another aspect, a hybrid sensor according to the present disclosure includes a sensor having a permanent magnet adjacent a permeable pole piece and a sensor coil coupled to the pole piece, the permeable pole piece may fabricated as a cylinder, the permeable pole piece has a concentric axis, the sensor coil is a spiral coil surrounding the permeable pole piece along the concentric axis of the permeable pole piece, a target for interacting with the sensor is provided, an excitation apparatus is connected to the sensor coil, the excitation apparatus is an inductive bridge, a temperature compensation coil may be coupled across the inductive bridge and may be located in the sensor or any other suitable location and an output signal detector connected to the excitation apparatus for determining sensor output, the output signal detector correlates the sensor output to a target surface velocity measurement.  
         [0015]     These and other features and advantages of this invention will become further apparent from the detailed description and accompanying figures that follow. In the figures and description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and the description.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a block diagram of a conventional variable reluctance sensor.  
         [0017]      FIG. 2  is a block diagram of a conventional variable inductance proximity sensor.  
         [0018]      FIG. 3  is a block diagram of a conventional induction speed sensor.  
         [0019]      FIG. 4A  is a block diagram of a hybrid variable inductance sensor according to the present disclosure.  
         [0020]      FIG. 4B  is a block diagram of an alternate embodiment sensor according to the present disclosure.  
         [0021]      FIG. 5  is a block diagram of an alternate embodiment hybrid sensor according to the present disclosure.  
         [0022]      FIG. 6A  is a block diagram of an alternate embodiment sensor according to the present disclosure.  
         [0023]      FIG. 6B  is a side view of the sensor of  FIG. 6A .  
         [0024]      FIG. 7A  is a block diagram of another alternate embodiment sensor according to the present disclosure.  
         [0025]      FIG. 7B  is a side view of the sensor of  FIG. 7A .  
         [0026]      FIG. 8  is a schematic diagram of the hybrid variable inductance sensor of  FIG. 4A .  
         [0027]      FIG. 9  is schematic diagram of the alternate embodiment sensor of  FIG. 5 .  
         [0028]      FIG. 10  is a graph of laboratory test data of a hybrid variable inductance sensor according to the present disclosure.  
         [0029]      FIG. 11  is a comparison plot of rotational speed versus time during a test measuring a rotating shaft slowing from 600 rpm&#39;s to zero rpm&#39;s as measured by a conventional sensor and a hybrid variable inductance sensor according to the present disclosure.  
     
    
     DETAILED DESCRIPTION  
       [0030]     Referring now to  FIG. 4A  and  FIG. 8 , in a currently preferred embodiment of the present disclosure, hybrid inductive sensor  10  includes excitation means  12 , permanent magnet  14 , pole piece  16 , and sensor coil  18  for sensing target surface velocity and or proximity to target  20 . Permanent magnet  14  may be any suitable material providing sufficient low frequency field strength such as a permanent magnet or a electromagnet. Pole piece  16  may be of any suitable permeable and/or conductive material exhibiting a low retained magnetization such as iron, steel, or nickel. Pole piece  16  may also be somewhat diamagnetic as a function of frequency.  
         [0031]     There are numerous materials that appear diamagnetic when exposed to a changing magnetic field. Many conductive materials exhibit an apparent diamagnetism. The mechanism by which a changing magnetic field induces a voltage in a pickup coil is replicated to a lesser or greater degree in any solid conductive material such as a block of copper. The apparent diamagnetism may vary due to magnetic field changes according to the rate of magnet movement.  
         [0032]     Typically, surface velocity or proximity measurement of a target, such as rotating machinery, requires a periodic feature or features on the rotating member scrutinized by the speed sensor. This is true for the vast majority of velocity sensing situations regardless of the speed sensor technology employed. For example, referring to  FIG. 4A , features  20 F are simply machined into a shaft, such as target  20 . A suitable target, such as target  20 , may incorporate one or more features  20 F as required, achieving the desired resolution.  
         [0033]     Both permanent magnet  14  and pole piece  16  may be configured as cylinders with a concentric axis  82  or any other suitable shape may be used. Sensor coil  18  may be any suitable material such as copper or other conductive material.  
         [0034]     Referring now to  FIG. 4B , an alternate embodiment of sensor  22 , pole piece  17  may be configured as a hollow cylinder shape with sensor coil  19  wound along the concentric axis  84  of pole piece  17 , within pole piece  17 .  
         [0035]     Referring now to  FIG. 8 , the addition of an excitation means  12 , such as an inductive bridge  58  to a variable reluctance sensor, effectively transforms it into a low speed or zero speed sensor and or a proximity sensor. The inductance of sensor coil  18  varies with the distance D between target  20  and sensor  22 . This occurs even if the proximity, distance D between target  20  and sensor  22  changes very slowly. In a typical application, an AC voltage  60  is applied across bridge  58  incorporating sensor coil  18  in sensor  22 , causing an AC current  62  to flow through sensor coil  18 , thus energizing sensor coil  18 . A comparison of AC current  62  with AC voltage  60  by output signal detector  86  generates sensor output  88  to monitor inductance of sensor  22  as influenced by target  20  and thus measure proximity between sensor  22  and target  20 . The details of output signal detector  86  depend on the technology employed, and any suitable technology may be used. Excitation means  12  may include an inductive bridge circuit, Colpitts Oscillator, or some other suitable type of coil driving circuit or apparatus. Temperature compensation coil  59  may also be used to improve the performance of hybrid inductive sensor  10 . Temperature compensation coil  59  may be included in sensor  22  or in any other suitable location.  
         [0036]     A common technique may be to monitor the phase between AC voltage  60  and AC current  62  and render the phase difference as proximity data. Another popular technique may be for sensor coil  18  to be a portion of a resonant circuit in excitation means  12  and use changes in frequency and/or amplitude that result from changes in inductance of sensor  22  measured by output signal detector  86  to provide speed or proximity sensor output  88 . Addition of excitation means  12  to a variable reluctance sensor may form a hybrid sensor with capability to penetrate through thicker metal housings such as housing  66  or span larger gaps than the variable inductance proximity sensor or sense low speed or zero speed and provide better proximity measurement.  
         [0037]     Referring now to  FIGS. 6A and 6B , in another embodiment of a hybrid inductive sensor according to the present disclosure, induction sensor  102  has as its target one or more permanent magnets  90  secured or otherwise incorporated in or on target  98 . When permanent magnet  90  is brought into the proximity of sensor  102 , sensor field  96  may be influenced by magnetic field  97 . Thus, the magnetization of pole piece  92  may be influenced, changing the response of pole piece  92  to high frequency field  96  coming from sensor coil  94  as excited by excitation circuit  104 . Sensor  102  may provide more efficient use of magnetic field  97 , resulting in lower flux leakage than sensors  22  and  70 .  
         [0038]     Referring now to  FIGS. 7A and 7B , in another embodiment of a hybrid inductive sensor according to the present disclosure, hybrid inductive sensor  118  includes excitation means  120 , permanent magnet  114 , pole piece  110 , and sensor coil  112  for sensing surface velocity of target  108 . One or more targets  108  may be included on rotor  109 . Target  108  may be any suitable variation in rotor  109  such as castellations, holes, depressions or other variations of rotor  109 . Permanent magnet  114  may be any suitable material providing sufficient low frequency field strength. Pole piece  110  may be of any suitable permeable and/or conductive material exhibiting a low retained magnetization. Sensor  118  may provide more efficient control of magnetic flux  106 , resulting in lower flux leakage than sensors  22  and  70 .  
         [0039]     A scrutinized target such as target  20  of  FIG. 4A , target  68  of  FIG. 5 , target  98  of  FIGS. 6A and 6B  or target  108  of  FIGS. 7A and 7B  may be rotating and or translocating. Referring to  FIG. 4A , Pole piece  16  is generally fabricated as a cylinder with a spiral coil surrounding pole piece  16  along its concentric axis  82 , such as sensor coil  18 .  
         [0040]     Referring now to the alternate embodiment of  FIGS. 6A and 6B , pole piece  92  is generally fabricated in a caliper shape with a spiral coil such as sensor coil  94  surrounding pole piece  92  along axis  100 .  
         [0041]     Referring now to the other alternate embodiment of  FIGS. 7A and 7B , pole piece  110  is generally fabricated in a caliper shape with a spiral coil such as sensor coil  112  substantially surrounding pole piece  110  along axis  116 . Permanent magnet  114  may be adjacent to pole piece  110  at location  110 A surrounded by sensor coil  112 .  
         [0042]     Pole pieces  16 ,  17 ,  92  and  110  are usually fabricated from magnetically permeable material. Any suitable material that typically exhibits a low retained magnetization may be used to fabricate pole piece  16 ,  17 ,  92  and  110 . A suitable material may also exhibit a high permeability in the field range being employed. Sensor coil  18 ,  94  and  112  may be single layer or multiple layers and one channel or multiple channels.  
         [0043]     Permanent magnet  14  is typically cylindrical shaped. It may be fabricated from magnetically permeable material that exhibits a relatively high retained magnetization.  
         [0044]     Referring now to  FIG. 5  and  FIG. 9 , in another embodiment of a hybrid inductive sensor according to the present disclosure, instead of utilizing a permanent magnet in sensor  22  as discussed above, induction sensor  70  has as its target a permanent magnet  72  secured or otherwise incorporated in or on target  68 . When permanent magnet  72  is brought into the proximity of sensor  70 , sensor field  74  is influenced by magnetic field  76 . This influences the magnetization of pole piece  16  thus changing the way pole piece  16  responds to high frequency field  74  coming from sensor coil  18  as excited by excitation circuit  12 .  
         [0045]     Field  76  of permanent magnet  72  has a lower frequency and a greater range than high frequency magnet field  74  generated by sensor coil  18  in sensor  70 . The lower frequency and greater range of field  76  may traverse a larger gap  80  between sensor  70  and target  68  than the high frequency magnetic field of sensor coil  18 .  
         [0046]     The high carrier frequencies associated with the common variable inductance sensor generate high-frequency fields that have difficulty penetrating through significant quantities of metal such as case  78 . The hybrid combination of a variable-reluctance style or induction style pole piece  16  with a variable inductance excitation circuit such as excitation means  12  significantly increases metal penetration because high frequency magnetic field  74  no longer has to penetrate through the metal. It only has to sense pole piece  16  whose permeability may be affected at much lower frequencies by field  76  from permanent magnet  72 .  
         [0047]     Referring now to  FIG. 4A  and  FIG. 5 , the high frequency fields associated with variable inductance excitation do not need to pass through housing materials such as housing  66  or case  78  to monitor a far away shaft even when separated by significant housing material thickness. They need only detect the changes in pole piece  16  which are driven by stronger low frequency fields associated with permanent magnet  14  or permanent magnet  72  either in the sensor and influenced by the shaft or in or on the target itself, respectively. Low frequency magnetic fields produced by permanent magnets have much greater housing material penetration and gap crossing reach.  
         [0048]     At least one permanent magnet  72  may be located on the surface of target  68 , embedded into the surface of the target, located inside a hollow target, or in any other suitable configuration. Sensor resolution of both speed and position may be increased with the use of multiple permanent magnets on a target. Multiple permanent magnets such as magnet  72  would induce more frequent changes in the pole piece high frequency magnetic field  74  during target translocation allowing more frequent measurement of target  68  than possible using a single permanent magnet.  
         [0049]     Referring now to  FIG. 10 , the result of a lab test in which target  20  is configured as a rotating shaft with four embedded features  20 F, as shown in  FIG. 4A , is trace  50 . The recorded pulses P are in groups, with each group  52  of four pulses P indicating a complete revolution of target  20 . The differing height H of the pulses indicate the varying distance D of a feature  20 F from sensor  22  during the test. The shorter the distance  34  between peaks, the faster target  20  is rotating. Slope  24  of pulse P is steeper than slope  26  that is steeper than slope  28 , thus the steeper slope of pulse P may be indicative of faster recorded rotational speed. Trace  50  indicates that target  20  is slowing from more than 120 rpm&#39;s at point  30  to zero rpm&#39;s at point  32 . Trace  50  has no amplitude or height H along section  36  indicating that target  20  stopped with sensor  22  between features  20 F. Time  38  indicates the time required for the shaft to rotate a quarter turn. Trace  50  shows that a hybrid inductive sensor according to this disclosure may enable accurate speed measurement over a span as short as a quarter turn as opposed to a full rotation or longer for conventional variable reluctance sensors. Varying height  39  of the pulses indicate that a hybrid inductive sensor according to this disclosure may also function as a proximity sensor.  
         [0050]     Referring now to  FIG. 11 , graph  40  depicts rotational speed versus time during the measurement of target  20  slowing from 600 rpm&#39;s to zero rpm&#39;s. Plot  42  is the plotted output data of a conventional variable reluctance sensor. Plot  44  is the plotted data of a hybrid inductive sensor according to this disclosure. Slope  48  of a plot, such as plot  44 , at any point such as point  46 , represents the net torque of decelerating target  20 . The slope of plot  44  changes as the rotational speed of target  20  changes from 200 rpm&#39;s to zero rpm&#39;s. The actual torque below 200 rpm&#39;s was previously unknown when measured by conventional flight approved sensors. A hybrid inductive sensor according to this disclosure allows real-time calculation of torque  54  at speeds below accurate measurement by conventional flight approved devices. Slope  48  indicates that the torque of decelerating target  20  near zero rpm is 15 inch-pounds.  
         [0051]     Having now described the invention in accordance with the requirements of the patent statutes, those skilled in this art will understand how to make changes and modifications in the present invention to meet their specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention as set forth in the following claims and their legal equivalents.