Linear variable displacement transformer (LVDT) with improved linearity using extreme end booster winding

A linear variable displacement transformer (LVDT) position sensor. The position sensor comprises a bobbin, a primary coil of wire wound on the bobbin, a first secondary coil wound in stepped layers on the bobbin, and a second secondary coil wound in stepped layers on the bobbin. The first secondary coil comprises a plurality of booster windings at an end of the first secondary coil. The second secondary coil comprises a plurality of booster windings at an end of the second secondary coil opposite the end of the first secondary coil booster windings. The stepped windings of the second secondary coil are complementary to the stepped windings of the first secondary coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Linear variable displacement transformer (LVDT) position sensors comprise a primary transformer coil winding and two secondary transformer coil windings wound on a common axis. As the primary transformer winding is excited with an alternating current (AC) voltage signal, it generates a magnetic field that couples into the two secondary transformer windings, establishing an AC voltage signal across the two secondary windings. A moveable core that is free to move linearly along the common axis of the windings affects the amount of magnetic coupling between the primary windings and each of the secondary windings. The moveable core is attached to a rod that is itself attached to some mechanical structure whose position is desired to be determined by the LDVT position sensor. As the moveable core moves in one direction or another, the coupling from the primary winding to the secondary windings changes, and an indication of the position is provided by the outputs of the secondary windings.

SUMMARY

In an embodiment, a linear variable displacement transformer (LVDT) position sensor is disclosed. The position sensor comprises a bobbin, a primary coil of wire wound on the bobbin, a first secondary coil wound in stepped layers on the bobbin, and a second secondary coil wound in stepped layers on the bobbin. The first secondary coil comprises a plurality of booster windings at an end of the first secondary coil. The second secondary coil comprises a plurality of booster windings at an end of the second secondary coil. The stepped windings of the second secondary coil are complementary to the stepped windings of the first secondary coil.

In another embodiment, a linear variable displacement transformer (LVDT) position sensor is disclosed. The position sensor comprises a bobbin, a primary coil comprising wire wound on the bobbin, a first stepped secondary coil comprising wire wound on the bobbin, and a second stepped secondary coil comprising wire wound on the bobbin. A first end of the first stepped secondary coil comprises more turns of wire than a second end of the first stepped secondary coil, and the first stepped secondary coil comprises a plurality of booster windings at the first end of the first stepped secondary coil. A first end of the second stepped secondary coil comprises fewer turns of wire than a second end of the second stepped secondary coil. The second stepped secondary coil comprises a plurality of booster windings at the second end of the second stepped secondary coil. The first end of the first stepped secondary coil is proximate to the first end of the second stepped secondary coil, and the second end of the first stepped secondary coil is proximate to the second end of the second stepped secondary coil.

In yet another embodiment, a linear variable displacement transformer (LVDT) position sensor is disclosed. The position sensor comprises a bobbin, a moveable core, and a primary coil of wire wound on the bobbin. The position sensor further comprises a first secondary coil wound in stepped layers on the bobbin and comprising a plurality of booster windings at an end 20% of the first secondary coil and a second secondary coil wound in stepped layers on the bobbin and comprising a plurality of booster windings at an end 20% of the second secondary coil opposite the end of the first secondary coil booster windings, where the stepped windings of the second secondary coil are complementary to the stepped windings of the first secondary coil.

DETAILED DESCRIPTION

The present disclosure teaches a linear variable displacement transformer (LVDT) position sensor with stepped complementary secondary coils that each has booster windings at one end. These booster windings can compensate for end effects of the coupling between the primary coil and the two secondary coils so as to extend the linear transducing range of the LVDT by as much as 20% and at the same time increase the accuracy of the LVDT over the entire transducing range. The effect of the booster windings may be conceptualized as compensating a voltage versus voltage (V/V) curve of the LVDT by making the curve more linear in an already linear portion of the curve and extending the linear range.

An LVDT may comprise secondary coils that are step wound such that a first end of a first secondary coil has more winding turns than a second end of the first secondary coil, and a first end of a second secondary coil has fewer winding turns than a second end of the second secondary coil, where the first ends of each secondary coil overlay and the second ends of each secondary coil overlay. The stepping of the windings taper each of the secondary coils but in opposite directions. A secondary coil winding may comprise a plurality of steps, where the number of winding loops or turns within each step is different from the number of winding loops in the other steps of that secondary coil. The number of winding loops in each step may increase monotonically from one end of the secondary coil to the opposite end of the secondary coil. In an embodiment, the number of winding loops in adjacent steps may differ by a constant value or by a constant delta. Thus, a second step of a secondary coil may comprise 60 more turns than a first step of the same secondary coil; a third step of the secondary coil may comprise 60 more turns than the second step of the same secondary coil; a fourth step of the secondary coil may comprise 60 more turns than the third step of the secondary coil; and so forth. This monotonically increasing number of winding loops or turns in a secondary coil may be said to produce a tapered secondary coil. A conventional tapering scheme of secondary coils in a LVDT position sensor features a constant delta number of turns between each adjacent step including the steps at the extremes of the secondary coil.

The present disclosure teaches adding a booster winding at one extreme or end of each secondary coil, where the booster winding breaks the pattern of increasing a constant delta number of windings between adjacent steps of the secondary coil. The booster winding is added at the end of the secondary coil that has the most number of turns. A booster winding is added to both the first secondary coil and the second secondary coil. Because the taper of the first and second secondary coils are tapered in opposite directions, the booster winding of the first secondary coil is at a first end of the LVDT, and the booster winding of the second secondary coil is at a second end of the LVDT, opposite to the first end of the LVDT. These relationships will be more clearly understood with reference to figures as described below.

Turning now toFIG. 1, a linear variable displacement transformer (LVDT) position sensor10is described. In an embodiment, the LVDT position sensor10comprises a bobbin12, a primary coil14, a first secondary coil16, a second secondary coil18, first booster windings20, and second booster windings22. In an embodiment, the LVDT position sensor10further comprises a moveable core26coupled to a connecting rod28. It is understood that in some embodiments, the LVDT position sensor10may be provided as a package or product that does not include the moveable core26and the connecting rod28. Alternatively, in some embodiments, the LVDT position sensor10may be provided as a package or product that does include the moveable core26and the connecting rod28. As known by one skilled in the art, electrical coils comprise a plurality of turns of conducting wire. In the LVDT position sensor10, the primary coil14, the secondary coils16,18, and the booster windings20,22are wound on the bobbin12that serves as a mechanical structure for the winding of turns of conducting wire.

The first secondary coil16and the second secondary coil18are both taper wound, but tapered in opposite senses. Thus, as illustrated, a left end of the first secondary coil16has more winding turns than a right end of the first secondary coil16and is tapered left to right; while a right end of the second secondary coil18has more winding turns than a left end of the second secondary coil18and is tapered right to left. In an embodiment, the tapering of the secondary coils16,18is accomplished by varying the spacing between the turns of the windings from one end to the opposite end of the bobbin12. The spacing between turns may be changed by constant amounts over each of a plurality of segments of the secondary coils16,18. The different spacing between turns in the different segments of the secondary coils16,18may be said to define the secondary coils16,18as stepped secondary coils. While the taper of the secondary coils16,18is illustrated as varying in thickness continuously from one end to another (in different senses for the first secondary coil16versus the second secondary coil18), in an embodiment, the number of turns over different segments of the secondary coils16,18vary not continuously but rather in discrete steps. Additionally, as discussed further hereinafter, the windings of the secondary coils16,18may be commingled as they are each wound in four layers using a crisscross winding technique.

The first booster windings20are electrically part of and a continuation of the first secondary coil16located at the extreme left end of the first secondary coil16. The second booster windings22are electrically part of and a continuation of the second secondary coil18located at the extreme right end of the second secondary coil18. Said in other words, the first secondary coil16and the first booster windings20form a third secondary coil, and the second secondary coil18and the second booster windings22form a fourth secondary coil.

When installed for use in a typical electromechanical system, the LVDT position sensor10provides an indication of a position of a structure that is coupled to the connecting rod28. Examples of aerospace applications of LVDT position sensors include use in flight control actuators, nose wheel steering systems, cockpit controls, engine bleed air systems, fuel controls, fly-by-wire systems, brake-by-wire systems, and environmental control systems. LVDT position sensors may be used in power turbine applications. LVDT position sensors can provide high repeatability and reliability.

In use, an excitation signal is applied to the primary coil14that generates a magnetic field that couples into the secondary coils16,18and the booster windings20,22and induces a response at the terminal or terminals of the coils16,18and/or the booster windings20,22. For example, an alternating current (AC) voltage is applied to the primary coil14by an external circuit (not shown). The coupling between the primary coil14and the secondary coils16,18and the booster windings20,22are modified by the position of the moveable core26. The moveable core26comprises a material that has relatively high magnetic permeability, such as ferro-magnetic materials. The moveable core26may comprise alloys of iron, nickel, cobalt, manganese, chromium, molybdenum, and/or combinations thereof. The moveable core26may comprise permalloy and/or mu-metal.

Not wishing to be bound by theory, because the secondary coils16,18are tapered in opposite directions, the moveable core26couples the magnetic field generated by the primary coil14into the secondary coils16,18and booster windings20,22differentially. Said in other words, the voltage induced in the first secondary coil16and first booster windings20is greater when the moveable core26is displaced to the left of center and less when the moveable core26is displaced to the right of center. Likewise, but in opposite sense, the voltage induced in the second secondary coil18and second booster windings22is less when the moveable core26is displaced to the left of center and greater when the moveable core26is displaced to the right of center. The change in the voltages induced in the coils16,18and booster windings20,22may be analyzed by external circuitry (not shown) to determine a position of the moveable core26and hence to determine a position of a mechanical structure coupled by the connecting rod28to the moveable core26.

The first secondary coil16and the second secondary coil18are uniformly tapered, that is the number of turns of windings forming the secondary coil increases by a constant delta from a first end to a second end. The first booster windings20connected to the first secondary coil16, however, make the extreme left end of the third coil (i.e., the combination of the first secondary coil16and the first booster windings20) non-uniformly tapered at its extreme left end. The second booster windings22connected to the second secondary coil18, likewise, make the extreme right end of the fourth coil (i.e., the combination of the second secondary coil18and the second booster windings22) non-uniformly tapered at its extreme right end.

The non-uniform taper of the third coil at its extreme left end adapts a response of the third coil to keep the position indication output of the third coil linear with position of the moveable core26further or over a greater range of displacement than the first secondary coil16without the inclusion of the first booster windings20. Without wishing to be bound by theory, it is thought that the addition of the first booster windings20corrects an error in the indication of position provided by the first secondary coil16in isolation that results from magnetic coupling edge effects when the moveable core26is displaced towards the left side. In a complementary manner, the non-uniform taper of the fourth coil at its extreme right end adapts a response of the fourth coil to keep the position indication output of the fourth coil linear with position of the moveable core26further or over a greater range of displacement than the second secondary coil18without the inclusion of the second booster windings22. In some contexts, the profile of windings of the first secondary coil16combined with the first booster windings20may be said to be complementary to the profile of windings of the second secondary coil18combined with the second booster windings22, in that the tapering of the third coil (the combination of the first secondary coil16and the first booster windings20) is similar in profile but opposite in sense to the tapering of the fourth coil (the combination of the second secondary coil18and the second booster windings22).

In an embodiment, the first booster windings20are provided in a 20% portion of the first secondary coil16on its left end; and the second booster windings22are provided in a 20% portion of the second secondary coil18on its right end. In another embodiment, the first booster windings20are provided in a 15% portion of the first secondary coil16on its left end; and the second booster windings22are provided in a 15% portion of the second secondary coil18on its right end. In another embodiment, the first booster windings20are provided in a 10% portion of the first secondary coil16on its left end; and the second booster windings22are provided in a 10% portion of the second secondary coil18on its right end.

The use of booster windings at the extreme ends of the secondary coils in the LVDT position sensor10can be conceived to extend the linear transducing range of a sensor or, alternatively, to reduce the size of a sensor. The LVDT position sensor10may also increase the accuracy of the position sensing across the entire range of the transducer relative to a LVDT position sensor having uniformly tapered secondary coils.

Turning now toFIG. 2, an electrical schematic40of the LVDT position sensor10is described. The electrical schematic40comprises the primary coil14having first terminal42; the first secondary coil16and the first booster windings20(the third coil) and the second secondary coil18and the second booster windings22(the fourth coil) having second terminal44. In an embodiment, the secondary coils16,18and booster windings20,22may have different terminations; for example, a center tap where the third coil and the fourth coil connect. When the first terminal42is stimulated with an appropriate AC excitation voltage, the voltage in the second terminal44provides an indication of a position of the moveable core26.

Turning now toFIG. 3, a second LVDT position sensor100is described. In an embodiment, the second LVDT position sensor100comprises stepped secondary windings. In an embodiment, the second LVDT position sensor100comprises a bobbin102, a primary coil104, a first secondary coil, a second secondary coil, a first booster winding118, and a second booster winding132. The first secondary coil comprises a plurality of stepped winding segments; for example, a first secondary coil first segment106, a first secondary coil second segment108, a first secondary coil third segment110, a first secondary coil fourth segment112, a first secondary coil fifth segment114, and a first secondary coil sixth segment116. The second secondary coil comprises a plurality of stepped winding segments; for example, a second secondary coil first segment120, a second secondary coil second segment122, a second secondary coil third segment124, a second secondary coil fourth segment126, a second secondary coil fifth segment128, and a second secondary coil sixth segment130. The secondary coil segments may also be referred to as steps.

It is understood that in different embodiments, the first and secondary coils may comprise a different number of winding segments; for example, each secondary coil comprising 3 winding segments, each secondary coil comprising 4 winding segments, each secondary coil comprising 5 winding segments, each secondary coil comprising 10 winding segments, or each secondary coil comprising some other number of winding segments. Said in a different way, in different embodiments, the secondary coils may comprise at least 3 steps, at least 4 steps, at least 5 steps, at least 6 steps, at least 10 steps, or some other number of steps. In an embodiment, the first secondary coil and the first booster winding118are formed of a first continuous length of wire, and the second secondary coil and the second booster winding132are formed of a second continuous length of wire. In another embodiment, however, the coils and windings may be made from connected multiple segments of wire. The number of turns in each winding segment is varied by varying the space between windings. It is the different number of turns in each different winding segment which is referred to as stepping or stepped.

In an embodiment, the first secondary winding is wound by winding in a first layer left to right, a second layer from right to left, a third layer from left to right, and a fourth and final layer from right to left. In an embodiment, the second secondary winding is wound by winding in a first layer right to left, a second layer from left to right, a third layer from right to left, and a fourth and final layer from left to right. In each layer, the spacing of the windings is varied to produce a desired taper and/or stepped number of turns in the subject segment. In an embodiment, the secondary coils are wound using a crisscross technique. The winding of the first booster windings118may be completed after the first secondary winding segments106-116have been wound, and the second booster windings132may be completed after the second secondary winding segments120-130have been wound. Alternatively, the booster windings118,132may be established by increasing the number of windings in the appropriate step or segment of the secondary windings; for example, by decreasing the spacing between turns in the first secondary coil first segment106and by decreasing the spacing between turns in the second secondary coil first segment120, whereby to provide a surplus number of turns in the associated secondary coils relative to a uniform taper configuration. It is understood that the windings of the first secondary coil and the second secondary coil will be intermingled and not vertically separated as illustrated inFIG. 3. The vertical layering of secondary coils inFIG. 3is thought to promote improved understandability of the construction of the LVDT position sensor100.

As an example, the primary coil104may comprise 2500 turns, the first secondary coil may comprise 900 turns, the second secondary coil may comprise 900 turns, the first booster winding118may comprise 50 turns, and the second booster winding132may comprise 50 turns. The first secondary coil first segment106comprises 300 turns, the first secondary coil second segment108comprises 240 turns, the first secondary coil third segment110comprises 180 turns, the first secondary coil fourth segment112comprises 120 turns, the first secondary coil fifth segment114comprises 60 turns, and the first secondary coil sixth segment116comprises zero turns or one turn. The second secondary coil first segment120comprises 300 turns, the second secondary coil second segment122comprises 240 turns, the second secondary coil third segment124comprises 180 turns, the second secondary coil fourth segment126comprises 120 turns, the second secondary coil fifth segment128comprises 60 turns, and the second secondary coil sixth segment130comprises zero turns or one turn. It will be appreciated that this configuration is provided for the sake of example and that the teachings of the present disclosure are applicable to a wide range of different configurations. It is understood that the booster windings are added to each extreme end of its corresponding secondary winding and constitutes an excess of windings or an increase of windings of at least 10%, of at least 15%, or of at least 20% relative to the extreme end winding segment with reference to a uniform taper and/or with reference to a constant delta of number of turns per segment. In an embodiment, the primary coil104, the first secondary coil, and the second secondary coil may each be about 2.4 inches in length, the moveable core140may be about 1.3 inches long, and the stroke of the moveable core140may be about 1 inch. The moveable core140may be mechanically coupled to an external structure by the connecting rod142.

A use may comprise the following steps. Step one, applying an excitation voltage to the primary coil, whereby the primary coil establishes a time varying magnetic field that links with the first secondary coil and the second secondary coil. Step two, locating the core in the center of the turns of the primary coil, the turns of the first secondary coil, and the turns of the second secondary coil (the coils are wound on a common axis or center, for example on the bobbin). Step three, outputting a response voltage from the first secondary coil and the second secondary coil in response to the time varying magnetic field that links from the primary coil. Step four, processing the output of the secondary coils to determine a linear position of the core. It is observed, as the core moves linearly in the center of the primary and secondary coils, the core alters the magnetic coupling from the primary coil to the secondary coils. Because the secondary coils are stepped and/or tapered, the magnetic coupling to the first coil is different from the magnetic coupling to the second coil when the core is displaced from a centered or neutral position. Because of the presence of booster windings on each of the extremes of the secondary coils, the range of linear response of the sensor is extended relative to the linear response range of a conventional (e.g., prior art) linear variable displacement transformer of like length. It is understood that the steps of this method may be iterated or repeated. In an embodiment, the steps of the method are iterated many times per second, for example more than about 30 times per second, more than about 100 times per second, more than about 200 times per second, more than about 1000 times per second, or some other number of iterations per second. Some steps may be substantially continuous, for example the processing of step one, step two, and step three may be regarded as continuous. It is understood that this method may be employed with either of the LVDT position sensor10described above with reference toFIG. 1or the second LVDT position sensor100described above with reference toFIG. 3.