Reciprocating electromagnetic actuator

What is claimed is:

1. A reciprocating electromagnetic actuator comprising:

a reciprocator formed of ferromagnetic

material having a longitudinal axis; a stator having a longitudinal axis and mounted parallel relative to the axis of said reciprocator, said stator being formed of ferromagnetic material, said stator having a first surface facing said reciprocator, said stator further having a first slot of a first width therein opening to said first surface;

a first coil having at least a portion thereof disposed in said first slot;

said reciprocator having a second surface facing said first surface at a fixed distance therefrom, said fixed distance being defined as an air gap, said second surface having a second slot therein facing said first slot, said second slot having a second width, said second width being different than said first width, at least one overlap area being defined on each side of said first or second slot where said first and second surfaces directly front each other separated by said fixed air gap, said overlap areas being so disposed that motion of the reciprocator equally increases one overlap area and decreases another overlap area, whereby the total overlap area remains constant;

a second coil having at least a portion thereof disposed in said second slot;

means for generating a constant magnetic flux that passes through said reciprocator and said stator following a flux path that passes across said air gap through said overlap areas, bypassing said first and second slots on at least one side of said slots, said magnetic flux linking said first and second coils or not linking said first and second coils as a function of whether the magnetic flux bypasses said first and second slots on one side or the other; and

means for exciting said first coil with a first current for producing a first ampere-turns, and for exciting said second coil with a second current for producing a second ampere-turns, said first and second ampere-turns being equal in magnitude and opposite in polarity at all times, whereby any magnetic flux generated by said first ampere-turns is offset by an opposing magnetic flux generated by said second ampere-turns, and further whereby the total magnetic flux passing through said air gap remains constant regardless of the position of the reciprocator relative to the stator;

whereby a force is produced between said stator and said reciprocator that is proportional to magnitude of the current in said second coil.

2. The reciprocating electromagnetic actuator of claim 1 wherein said magnetic flux generating means comprises at least one permanent magnet mounted within said reciprocator.

3. The reciprocating electromagnetic actuator of claim 2 wherein said at least one permanent magnet is positioned within said reciprocator so as to cause the magnetic flux to pass longitudinally therethrough.

4. The reciprocating electromagnetic actuator of claim 3 wherein said first coil lies substantially in a plane that is perpendicular to the longitudinal axis of said reciprocator and said stator.

5. The reciprocating electromagnetic actuator of claim 2 wherein said at least one permanent magnet is positioned within said reciprocator so as to cause the magnetic flux to pass transversely therethrough.

6. The reciprocating electromagnetic actuator of claim 5 wherein said reciprocator includes a non-magnetic material near the center thereof.

7. The reciprocating electromagnetic actuator of claim 2 wherein said at least one permanent magnet has a polarity axis running from its north pole to its south pole that is skewed relative to the longitudinal axis of said reciprocator.

8. The reciprocating electromagnetic actuator of claim 1 wherein said first coil lies substantially in first plane that is parallel to the longitudinal axis of said reciprocator and said stator.

9. The reciprocating electromagnetic actuator of claim 8 wherein said second coil lies substantially in a second plane that is parallel to said first plane.

10. The reciprocating electromagnetic actuator of claim 1 wherein said magnetic flux generating means comprises at least one permanent magnet mounted within said stator.

11. The reciprocating electromagnetic actuator of claim 10 wherein said at least one permanent magnet is positioned within said stator so as to cause the magnetic flux to pass transversely through said reciprocator.

12. The reciprocating electromagnetic actuator of claim 11 wherein said reciprocator further includes a non-magnetic material disposed near the center thereof.

13. The reciprocating electromagnetic actuator of claim 11 wherein said first coil lies substantially in a first plane that is substantially parallel to the longitudinal axis of said stator.

14. The reciprocating electromagnetic actuator of claim 13 wherein said second coil lies substantially in a second plane that is substantially parallel to said first plane.

15. The reciprocating electromagnetic actuator of claim 1 wherein said magnetic flux generating means comprises four permanent magnets, each of a first pair of said magnets being disposed on opposite sides of a first end of said stator, and each of a second pair of said magnets being disposed on opposite sides of a second end of said stator, said magnets each having a magnetic polarity that causes magnetic flux to flow in said flux path in the same direction.

16. The reciprocating electromagnetic actuator of claim 1 further including means for cooling said stator and said reciprocator, whereby heat present in said stator and reciprocator can be dissipated.

17. The reciprocating electromagnetic actuator of claim 1 further including means for holding said stator stationary and for allowing said reciprocator to axially move back and forth within said stator.

18. The reciprocating electromagnetic actuator of claim 17 wherein said means for exciting said second coil with said second current includes:

a current source that generates said second current; and

conductive flexure means for electrically and continuously connecting said current source to said second coil regardless of the reciprocating motion of said coil as said coil moves within said reciprocator.

19. The reciprocating electromagnetic actuator of claim 18 wherein said conductive flexure means is further for mechanically supporting said reciprocator for reciprocating axial motion within said stator.

20. The reciprocating electromagnetic actuator of claim 1 wherein said first and second coils are connected in series, whereby said first current equals said second current.

21. A reciprocating electromagnetic actuator assembly comprising:

a plurality of actuator units physically stacked together, each of said units including:

a reciprocator formed of a material allowing magnetic flux to pass therethrough and having a longitudinal axis,

a stator having a longitudinal axis and mounted concentrically relative to said reciprocator, said stator being formed of a material allowing magnetic flux to pass therethrough, said stator having a surface facing said reciprocator, said stator further having a first slot of a first width therein opening to said surface,

a drive coil having at least a portion thereof disposed in said first slot,

said reciprocator having a second slot therein facing said first slot, said second slot having a second width, said second width being different than said first width,

a compensating coil having at least a portion thereof disposed in said second slot,

means for generating a magnetic flux that passes through said reciprocator and said stator following a flux path that bypasses said first and second slots on at least one side of said slots, said magnetic flux linking said drive coil or not linking said drive coil as a function of whether the magnetic flux bypasses said first slot on one side or the other, and

means for exciting said drive coil with a drive current and for exciting said compensating coil with a compensating current, said drive current and compensating current having respective polarities such that forces generated by the interaction of the magnetic flux linking said excited drive coil and excited compensation coil cause relative reciprocating axial motion at prescribed force levels between said stator and said reciprocator;

means for exciting the drive coils and compensating coils of each of said units with a desired drive current and compensating current at the same time; and p2 means for physically coupling the relative motion between the stators and reciprocators of all of said units in a way that adds the forces causing said motion together;

whereby the force generated by the reciprocating electromagnetic actuator assembly is substantially equal to the sum of the individual forces generated by each unit within said assembly.

22. A reciprocating electromagnetic actuator comprising:

a stator having spaced pole end pieces extending therefrom, each of said pole pieces including at least one slot;

a reciprocator assembly having spaced-apart magnetic portions supported for reciprocation adjacent said pole pieces, each of said magnetic portions having at least one slot facing a respective one of said pole pieces;

means for establishing a magnetic circuit through said pole pieces and through said reciprocator magnetic portions, said magnetic circuit having a magnetic flux of substantially constant magnitude;

a compensating coil positioned at least in part within the slots of said pole pieces;

a drive coil positioned at least in part within the slots of the magnetic portions of said reciprocator assembly;

means for exciting said drive coil with a drive current, thereby producing a drive coil ampere-turns;, and

means for exciting said compensation coil with a compensation current, thereby producing a compensation coil ampere-turns;

said drive ampere-turns and said compensation ampere-turns being of equal magnitude and opposite polarity at all times.

23. The reciprocating electromagnetic actuator of claim 22 wherein said means for exciting said drive coil includes:

current generating means for generating said drive current; and

conductive flexure means for electrically coupling said drive coil to said current generating means and for supporting said reciprocator assembly, including said drive coil, for reciprocation within said stator.

24. The reciprocating electromagnetic actuator of claim 22 wherein said means for establishing said magnetic circuit includes at least one permanent magnet mounted within said stator.

25. The reciprocating electromagnetic actuator of claim 24 wherein said means for establishing said magnetic circuit includes at least one permanent magnet mounted near each pole piece of said stator.

26. The reciprocating electromagnetic actuator of claim 25 further including means for cooling said actuator.

27. The reciprocating electromagnetic actuator of claim 26 wherein said cooling means comprises means for passing a heat transfer agent, such as a liquid, through portions of said stator and said reciprocator.

28. The reciprocating electromagnetic actuator of claim 22 wherein said means for establishing said magnetic circuit includes at least one permanent magnet mounted within each of the magnetic portions of said reciprocator assembly.

29. An reciprocating electromagnetic actuator comprising:

a stator assembly having spaced pole pieces extending therefrom, each of said pole pieces including at least one slot;

a reciprocator assembly supported for oscillation adjacent said pole pieces;

means for establishing a magnetic circuit loop through said stator assembly and through said reciprocator assembly, said magnetic circuit loop having a magnetic flux of substantially constant magnitude flowing therethrough;

a compensating coil positioned at least in part within the slots of said pole pieces;

a drive coil facing said compensating coil and embedded within said reciprocator assembly; and

means for exciting said drive coil with a drive current and said compensation coil with a compensation current so as to produce substantially equal ampere-turns in each coil at substantially the sam time.

30. The reciprocating electromagnetic actuator of claim 29 wherein said means for establishing a magnetic circuit loop includes at least one permanent magnet mounted within said armature assembly.

31. The reciprocating electromagnetic actuator of claim 30 wherein said permanent magnet has a magnetic axis that is skewed relative to the longitudinal axis of said armature assembly.

32. A reciprocating electromagnetic actuator comprising:

a stator;

a reciprocator;

at least one air gap between said stator and said reciprocator;

at least one source of magnetic flux;

at least one drive coil;

at least one compensating coil;

a drive electric current through said drive coil producing drive ampere-turns;

a compensating electric current through said compensating coil producing compensating ampere-turns; and

support structure for supporting said stator and said reciprocator with said air gap therebetween, said support structure including means for allowing said reciprocator to move relative to said stator in a direction parallel to said air gap;

said stator and said reciprocator having ferromagnetic portions;

said ferromagnetic portions, said source of magnetic flux, and said air gap comprising a magnetic circuit;

said air gap being divided into two parallel portions separated by slots in said stator and said reciprocator, one of said stator or reciprocator parallel portions overlapping the other of said stator or reciprocator parallel portions with two overlap areas so disposed that motion of the reciprocator equally increases one overlap area and decreases the other overlap area;

said drive coil and said compensating coil being disposed in said slots;

said compensating ampere-turns being substantially equal to and of an opposite polarity from said drive ampere-turns at all times;

whereby the magnetic flux density is said air gap is substantially constant regardless of reciprocator position or of current magnitudes; and

whereby a force is produced between said stator and said reciprocator proportional to said current and independent of the reciprocator position.

33. A reciprocating electromagnetic actuator comprising:

a reciprocator formed of a ferromagnetic material;

a stator also formed of a ferromagnetic material, the reciprocator being mounted for reciprocal motion relative to the stator;

means for generating a constant magnetic flux that passes through the stator and reciprocator;

a first coil disposed in the reciprocator through which a first current is passed, said first current creating a first magnetic flux that subtracts or adds to said constant magnetic flux; and

a second coil disposed in the stator through which a second current is passed, said second current creating a second magnetic flux that offsets the first magnetic flux, whereby the total magnetic flux passing through the stator and reciprocator remains constant.

34. The reciprocating electromagnetic actuator of claim 33 wherein the reciprocator and stator are mounted such that their respective longitudinal axes are parallel to each other, concentrically, so as to allow relative linear motion between the reciprocator and the stator.

35. The reciprocating electromagnetic actuator of claim 33 wherein the reciprocator and stator are mounted such that their respective axes of rotation are concentric, thereby allowing relative angular motion between the reciprocator and the stator.

36. The reciprocating electromagnetic actuator of claim 33 wherein the stator has a first pole piece in which a first slot of a first width is placed, the first coil passing through this first slot; and wherein the reciprocator has a second pole piece in which a second slot is placed, the second slot generally facing the first slot, the second slot having a second width different than the first width, the second coil passing through the second slot; and wherein the magnetic flux passes through the reciprocator and stator following a flux path that bypasses the first and second slots on at least one side of the slots, the magnetic flux thereby linking or not linking the first and second coils as a function of whether the magnetic flux bypasses the slots on one side or the other.

37. The reciprocating electromagnetic actuator of claim 36 further including means for exciting the first coil with said first current and for exciting the second coil with said second current, said second current and second coil being of equal ampere turns to said first current and first coil.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

The present invention relates to reciprocating electromagnetic actuators. More particularly, the present invention relates to a reciprocating electromagnetic actuator that produces instantaneous output forces over the full stroke or arc of the reciprocating device that are linearly proportional to an applied input current.

Electromagnetic actuator devices are known in the art that produce reciprocating motion. Such reciprocating motion may be either linear, i.e., back and forth along a straight-line axis; or angular, i.e., back and forth along a curved or arched axis. (It is noted that the term "linear" as used herein may have two separate meanings. When used to describe motion, "linear" refers to motion along a straight-line axis. When used to describe forces, "linear" refers to a proportional relationship between the output force of the device and an applied input current. More particularly, if F=kI, where F is the output force, I is the input current, and k is a constant, the output force is said to be "linear".) However, most are characterized by very small stroke, low frequency response, or low efficiency (low output power relative to the input power and weight/size of the device).

One of the most commonly known devices for producing linear motion is the voice coil motor. The voice coil motor typically includes an electric coil in the form of a thin wall cylinder that fits into a co-axial annular air gap in a magnetic circuit. The magnetic circuit includes a magnet (usually a permanent magnet) for generating magnetic flux that passes across the annular air gap. The voice coil is guided to move axially at right angles to the magnetic flux in the annular air gap.

While the voice coil motor offers the advantage of a relatively high frequency response, it suffers from numerous drawbacks. For example, because the voice coil is trapped in still air between the sides of the air gap, the coil exhibits poor heat dissipation. Further, the air gap thickness must equal or exceed the thickness of the coil plus mechanical clearances on each side. Large air gaps require large magnets in order to maintain the same forces that could be generated using small air gaps and smaller magnets. Typically, the coil is made thin to minimize magnet size at the expense of making the coil resistance high and making electrical heating correspondingly high.

Also known in the art for producing angular reciprocating motion is the d'Arsonval galvanometer. This device forms the basis for most DC voltmeters and ammeters. It is essentially the rotary equivalent of the voice coil motor. As such, it has the same advantages and disadvantages.

Still another type of device known in the art for producing linear motion is that shown in U.S. Pat. No. 3,336,488, invented by Scott, and that shown in U.S. Pat. No. 3,366,809, also invented by Scott. The Scott devices teach the use of a magnetic circuit having a stator with at least two pole pieces and an armature adapted for movement relative to the stator. Each pole piece has at least one slot therein, thereby forming at least two teeth in each pole piece through which the magnetic flux can flow. In particular, Scott teaches the concept of carefully spacing the teeth in the pole piece relative to the length of the armature segments facing the pole piece so that flux in the magnetic circuit is alternately transferred from one tooth to the next as the armature moves. The advantages of the Scott devices are that a long stroke can theoretically be achieved by simply increasing the number of teeth. However, the disadvantages of the Scott devices are that: (1) the flux density across the air gap does not remain constant as the armature moves; (2) the forces developed are thus non-linear (not proportional to input current); and (3) this non-linearity has the effect of adding a centering force to the intended force, as described below.

To illustrate, in the Scott devices the applied current superimposes a local magnetic flux on the main magnetic flux (from the permanent magnet). When the moving core (armature) is centered, the local flux is a maximum; but as soon as the core displaces, the local flux decreases. This is because the total reluctance of the local flux circuit is the sum of the reluctance on each side of the slot. The reluctance on the side with diminishing overlap approaches infinity as the moving core edge approaches the slot edge. Thus, the total reluctance of the local flux circuit also approaches infinity as the moving core edge approaches the slot edge. Thus, the total reluctance of the local flux circuit also approaches infinity, causing the flux density across the gap to decrease to zero as the core edge approaches the slot edge. This action, in turn, creates a non-linear output force which has the effect of centering the moving core between the two teeth at each end of the slot. Further, if large currents are applied to the Scott devices in an attempt to generate large forces, the iron will saturate and demagnetize the magnets.

In general, therefore, the Scott devices are useful only for applications where a non-linear output force is acceptable for generating reciprocating motion at relatively low output forces, such as in electric cutting devices. The Scott devices are totally inadequate for applications requiring a linear output force independent of the position of the moving core (armature), particularly where such forces must be large forces.

Another type of linear motion reciprocator known in the art is taught in U.S. Pat. No. 4,349,757, invented by Bhate. The Bhate device incorporates a series of carefully spaced permanent magnets on the armature, having alternating radially oriented polarities. The magnets are adjacent to the air gap. While the Bhate device offers some advantages, a careful examination thereof shows that the flux density at each point in each magnet rises and falls as that point is adjacent to a tooth or slot of the pole piece. That portion of the magnet opposite the slot is useless. Further, the rise and fall of the flux density tends to demagnetize the magnet. What is needed therefore, is a permanent magnet reciprocating device wherein the magnetic flux density remains constant, thereby providing linear forces and avoiding undesirable demagnetization.

SUMMARY OF THE INVENTION

The present invention provides a reciprocating electromagnetic actuator that develops true linear output forces independent of the position of its moving member relative to its non-moving member. The moving member, hereafter generally referred to as the "reciprocator," is mounted for reciprocating motion relative to the non-moving member, hereafter generally referred to as the "stator." Pole pieces in both the reciprocator and stator are positioned so as to face each other (hereafter this facing relationship may be referred to as "fronting") with a small air gap therebetween. The pole pieces comprise part of a magnetic path through which magnetic flux from a suitable source, e.g., a permanent magnet, may pass through one pole piece, across the narrow air gap, to the other pole piece. A drive coil, embedded within the reciprocator is positioned such that a portion thereof carries a drive current at right angles to the magnetic flux in the pole pieces, thereby developing a force according to well known electromagnetic principles. This force moves the reciprocator relative to the stator. A compensating coil, embedded within the stator, carries a compensating current equal in magnitude to the drive current, but of opposite polarity. Forces developed by interaction of the compensating current with the magnetic flux create no movement because the stator is held stationary. However, magnetic flux generated by the drive current is advantageously offset by magnetic flux generated by the compensating current, thereby maintaining the total magnetic flux in the magnetic circuit at a constant level, as generated by the permanent magnet. Further, the pole pieces are configured to maintain the total cross-sectional area fronting the air gap constant regardless of the position of the reciprocator relative to the stator over the full stroke distance of the reciprocator within the stator. Thus, the magnetic circuit reluctance does not change as the reciprocator moves, and the magnetic flux density across the air gap remains constant regardless of reciprocator's position within its defined stroke. This constant magnetic flux density advantageously allows output forces to be generated that are linearly proportional to the applied drive current, regardless of the position of the reciprocator along its defined stroke, thereby resulting in a truly linear electromagnetic actuator.

Advantageously, heat generated in the drive or compensating coils can be efficiently dissipated. Further, the air gap is not limited by the thickness of the coil, thereby allowing larger forces to be efficiently generated. Moreover, unlike some prior art devices, such as the Bhate device, a large number of permanent magnets are not required, either on the moving portions of the motor or the stationary portions.

The reciprocating electromagnetic actuator of the present invention thus includes a reciprocator formed of a ferromagnetic material, a stator also formed of a ferromagnetic material, the reciprocator being mounted for reciprocal motion relative to the stator, means for generating a magnetic flux that passes through the stator and reciprocator, a first coil disposed in the stator through which a first current is passed, and a second coil disposed in the reciprocator through which a second current is passed. In a linear motion embodiment, the reciprocator and stator are mounted such that their respective longitudinal axes are parallel to each other, concentrically, so as to allow relative linear motion between the two components. In an angular motion embodiment, the reciprocator and stator are mounted such that their respective axes of rotation are concentric, so as to allow relative angular motion between the two components. In either embodiment the stator has a first pole piece in which a first slot of a first width is placed. The first coil passes through this first slot. In turn, the reciprocator has a second pole piece in which a second slot is placed, the second slot generally facing or fronting the first slot. The second slot has a second width different than the first width. The second coil passes through the second slot. The magnetic flux passes through the reciprocator and stator following a flux path that bypasses the first and second slots on at least one side of the slots, the magnetic flux thereby linking or not linking the first and second coils as a function of whether the magnetic flux bypasses the slots on one side or the other. The invention further includes means for exciting the first coil with a first current and for exciting the second coil with a second current of equal ampere turns. The effect of the second coil is to reduce the self-inductance of the first coil to zero, thereby preventing the first current from creating magnetic flux that would add to or subtract from the magnetic flux already present in the flux path, which adding or subtracting of magnetic flux would undesirably affect the linearity of the actuator. Because the second coil effectively compensates for (reduces) the self-inductance of the first coil, the second coil is sometimes referred to as a "compensating" coil, and the first coil is referred to as a "drive" coil.

Advantageously, a feature of the present invention is that the means for generating the magnetic flux can be a one or more permanent magnets mounted within the reciprocator, the stator, or both. In one embodiment, the polar axis of such magnet(s) can be skewed relative to the longitudinal axes of the stator or reciprocator in order to maintain a desired flux density while reducing the overall physical dimensions of the core piece or pole piece components.

Still another feature of the invention allows a plurality of reciprocating electromagnetic actuators as above described to be stacked one on top of the other (or one next to the other), thereby effectively placing such actuators in parallel. The reciprocator of each stacked actuator can then be physically coupled to the other reciprocators of the other actuators in order to increase the force delivered.

As indicated above, it is a main feature of the present invention to provide an electromagnetic actuator that develops an output force at its moving member (reciprocator) that is linearly proportional to an applied drive current independent of the position of the moving member along its defined stroke length or arc.

It is another feature of the invention to provide an electromagnetic actuator having a reciprocator and stator with an air gap therebetween, and wherein the magnetic flux density across the air gap remains constant regardless of the position of the reciprocator relative to the stator.

A further feature of the invention advantageously allows magnets and currents of almost any size to be used in the construction of the reciprocating actuator, thereby making the actuator design adaptable to a wide variety of applications. Hence, for example, very large reciprocating forces can be efficiently developed through the use of relatively large magnets and currents, limited primarily only be heating. Further, if needed, the construction disclosed herein readily lends itself to the inclusion of cooling systems within the actuator in order to dissipate heat.

It is further noted that while the preferred embodiments of the invention described herein contemplate that the stator be held stationary and that the reciprocator be allowed to move, either component can be mounted for reciprocating movement relative to the other.

It is further noted that while the embodiments described herein relate generally to linear motion reciprocating electromagnetic actuators, rotary equivalents of such linear actuators also exist and could be readily fashioned by those skilled in the art from the descriptions presented herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages and features of the present invention will be more apparent from the following more particular description thereof presented in conjunction with the following drawings, wherein:

FIG. 1 is a diagrammatic illustration of a simplified embodiment of a reciprocating electromagnetic actuator made in accordance with the present invention;

FIG. 2 is an end view of the actuator of FIG. 1;

FIGS. 3 and 4 are partial diagrammatic illustrations similar to FIG. 1 showing the reciprocator in its respective furthermost left and right positions relative to the stator;

FIG. 5 shows the output force developed by the actuator of the present invention as a function of an input current having an irregular waveform;

FIG. 6 is a diagrammatic illustration of a skewed-magnet embodiment of the present invention;

FIG. 7 is a perspective view of a linear reciprocating actuator built in accordance with the teachings of the present invention;

FIG. 8 is a block diagram of the control and cooling systems used with the motor of the present invention;

FIG. 9 is a diagrammatic illustration of an alternative embodiment of the present invention;

FIG. 10 is a diagrammatic illustration of yet a further alternative embodiment of the invention, and illustrates how a plurality of such devices can be stacked together;

FIG. 11 is a diagrammatic illustration of still yet another embodiment of the motor of the present invention;

FIG. 12 is a partial diagrammatic illustration of a variation of the embodiment shown in FIG. 11;

FIG. 13A is an end view of the embodiment of FIG. 12, and also illustrates how this embodiment (as well as the embodiment of FIG. 11) can be selectively stacked;

FIG. 13B is a top view of the embodiment of FIG. 11 or FIG. 12, and further clarifies the orientation of the drive coil and compensation coil relative to the longitudinal axis of the motor;

FIG. 14 is a diagrammatic representation of yet another embodiment of the invention;

FIG. 15 is a partial end view of the embodiment of FIG. 14;

FIG. 16 illustrates water cooling of the embodiment of FIG. 14;

FIG. 17 diagrammatically illustrates the use of fluid both for cooling and for making electrical contact with the moving drive coil on the reciprocator;

FIGS. 18A, 18B and 18C detail one embodiment of a flexure mechanism used to make continuous electrical contact with the moving compensation coil; and

FIG. 19 is a simplified diagrammatic illustration of an angular embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best presently contemplated mode of practicing the invention. This description is not to be taken in a limiting sense but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be ascertained with reference to the appended claims.

Before describing the specific details of the various embodiments of the invention, a brief description of the fundamental operating principles upon which the invention depends may be helpful. Essentially, it is fundamental that when a conductor carrying a current is placed in a magnetic field, a force is exerted on the conductor. When the conductor is at right angles to the magnetic field, the force is at right angles to both the conductor and the magnetic field. The force generated is directly proportional to the flux density of the magnetic field, the length of the conductor in the field and the amount of current in the conductor. Because all the forces in a magnetic system must be balanced, per Newton's Third Law, when a force is exerted on a conductor, an equal and opposite force is exerted on the other elements of the system. Similarly, when magnetic flux is carried by iron that surrounds, or otherwise bounds, a conductor carrying a current, such as a coil embedded in a slot between teeth in the iron, a force is generated that is directly proportional to the flux density in the iron, the length of the conductor (number of turns in the slot), and the amount of current in the conductor.

It is also fundamental that a current carrying conductor generates a magnetic field around the conductor. The flux of this magnetic field may add to or subtract from the flux of any other magnetic field that is present, depending upon its direction. Current carrying conductors placed in a magnetic field can thus be used to selectively add flux at some points, and subtract flux at other points, thereby giving the effect of diverting the flux from one position to another, depending upon the strength of the prior-existing field and the direction of the current flow.

Finally, it is noted that the amount of magnetic flux in a magnetic circuit is related to the magnetic properties (reluctance) of the type of material in which the flux is found, just as the amount of current present in an electrical circuit is related to the electrical properties (impedance) of the material (conductors) in which the current flows. In general, certain magnetic materials (such as iron) exhibit low magnetic reluctance and allow magnetic flux to pass therethrough with less effort or energy (magnetomotive force) than do non-magnetic materials (plastic, wood, air). For example, if a given amount of magnetic flux is present in a magnetic circuit as forced by a given amount of magnetomotive force, and if such flux is presented with two parallel paths, one of air, the other of iron, almost all of the flux will travel through the iron. Therefore, if a segment of magnetic material, such as iron, is placed within an air gap of a magnetic circuit, the vast majority of the flux crossing the air gap will seek out and pas through the iron. If the segment of iron in the air gap is mounted such that it can freely move, and if the location at which the flux crosses the gap is changed, the segment of iron is forced towards the position at which the total flux is a maximum. Hence, if a current carrying conductor is selectively positioned within the magnetic circuit so as to selectively divert the location at which the most flux crosses the air gap from one location to another (as by changing the direction of the current flow), a movable segment of iron within the air gap can be made to reciprocate back and forth in synchrony with the flux diversion.

With the above fundamental electromagnetic principles in mind, reference is now made to FIGS. 1 and 2 wherein a diagrammatic illustration of one embodiment of a reciprocating electromagnetic actuator 20 made in accordance with the present invention is shown. The actuator includes a stator 22 secured to a stationary reference plane 24. The stator, as shown best in FIG. 2, includes four identical separate stator sections 26, 27, 28, and 29, one on each side of the stator, all securely mounted to each other and the reference plane 24, and all spaced equidistant from a longitudinal axis 30. Typically, each stator section is made from steel laminations 32a, 32b, etc., each made from silicon steel or transformer iron. Each of these stator sections are identical in construction and operation; hence, the description that follows is generally limited to just one stator section, usually the upper stator section 27.

Each of the stator sections 26-29 surround and define a centrally located core 34. A reciprocator 36, having a longitudinal axis 38, is mounted for reciprocating motion within the core 34. Preferably, once the reciprocator is mounted within the stator, the longitudinal axis 30 of the stator and the longitudinal axis 38 of the reciprocator are the same. That is, the reciprocator and stator are coaxial. Any suitable mounting technique could be used to perform this reciprocal mounting function, such as linear bearings, sliding or rolling bearings, or hydrostatic bearings. However, as shown in FIGS. 1 and 2, the preferred mounting technique is to use a flexure 40 at one end of the actuator and a similar flexure 42 at the other end of the actuator. Each of these flexures has one end securely fastened to the reference plane 24 and the other end fastened to one end of the reciprocator 36. The reciprocator 36 is supported within the core 34 by the flexures 40, 42 so as to maintain a substantially constant-width air gap 44 between facing sides of the reciprocator and stator.

As shown in FIG. 1, the reciprocator 36 includes a center section 52, made from a suitable solid ferromagnetic material. A permanent magnet 46, having a magnetic polar axis (north-south pole alignment) that is aligned with the longitudinal axes 30 and 38 of the stator and reciprocator, is positioned within the center section 52. At the left end of the center section 52, and as part of the reciprocator 36, are pole pieces 48, 49, 50 and 51, each facing the respective stator sections 26, 27, 28 and 29. Similar pole pieces 48', 49', 50' and 51' are located at the right end of the center section 52. These pole pieces 48-51 and 48'-51' are preferably made from silicon steel or transformer iron laminations in a manner similar to the construction of the rotator sections 26-29. The reciprocator 36, with its magnet 46, center section 52, and pole pieces 48-51 and 48'-51', in combination with the stator 22, including the stator sections 26-29, thus comprise a magnetic circuit in which magnetic flux is found. Adopting the convention of magnetic flux passing from the north pole to the south pole, and with the orientation of the magnet polarity shown in FIG. 1 (north pole on the left), it is seen that at least one flux path travels clockwise from the north pole of the magnet 46, through the center section 52, through pole piece 49, across the air gap 44, longitudinally through the stator section 27, back across the air gap 44, through pole piece 49', through the center section 52, and back to the south pole of the magnet 46. Two flux paths 54 and 56 are identified in FIG. 1 by dotted lines. The manner in which flux follows these paths will be explained below in connection with the description of FIGS. 3 and 4. Other flux paths, not shown, carry the flux from other pole pieces to the other stator sections.

Still referring to FIG. 1, it is seen that a slot 60 is placed in the left end of the stator 22, and a slot 62 is placed in the right end of the stator 22. Corresponding slots 60 and 62 pass through each section 26-29 of the stator 22. A compensating coil 64 is placed in the slot 60, and another compensating coil 66 is placed in the slot 62. These coils pass through each slot of each stator section, as best seen in FIG. 2. In practice, as is understood by those versed in the art, the coils 64 and 66 are typically connected in series, thereby forming a single compensating coil.

Similarly, a slot 68 is placed in each of the pole pieces 49-51, and another slot 70 is placed in each of the pole pieces 49'-51'. A drive coil 72 is placed in slot 68, so as to pass through each pole piece 49-51, and another drive coil 74 is placed in slot 70 so as to pass through each pole piece 49'-51-. The coil 72 is connected in series with the coil 74, thereby forming a single drive coil. Further, as explained below, the drive coil 72, 74 and the compensating coils 64, 66 are also preferably connected in series, thereby ensuing that the same current flows through both the drive coil and the compensating coil.

A note about the convention used herein to illustrate the coils 66 and 74 (or 64 and 72) is in order. First, following conventional practice, the current flowing in these coils is drawn as a "+" or a "x" if the current is flowing into the paper away from the observer (symbolic of the tail of an arrow), and as a dot, ".", if the current is flowing out of the paper towards the observer (symbolic of the point of an arrow). Second, for simplicity, only one turn is illustrated for the coils in the diagrammatic type figures presented herein. However, it is to be understood that any number of turns could be (and generally is) employed. (As is known to those skilled in the art, and ignoring secondary effects, the same current density, and hence the same magnetomotive force for magnetic circuit analysis purposes, results from using a single-turn coil having a given cross-sectional area as is obtained using a multi-turn coil, all the turns of which combine to give the same cross-sectional area.)

To illustrate, it is seen in FIG. 1 that the coil 64 has a current therein that is going into the paper at the top portion of the coil and is coming out of the paper at the bottom portion of the coil. Thus, the drive coil lies in a plane that is substantially perpendicular to the plane of the paper of FIG. 1, and perpendicular to the axis 30. Similarly, the compensation coil 72 has a current that flows out of the paper at the top of the coil and into the paper at the bottom of the coil.

Referring next to FIGS. 3 and 4, the operation of the actuator shown in FIGS. 1 and 2 will be explained. In FIG. 3, a portion of the diagrammatic illustration of FIG. 1 is shown with the reciprocator 36 at its extreme right position relative to the stator 22. In FIG. 4, the reciprocator 36 is at its extreme left position. As seen in FIG. 3, with the reciprocator at its right position, all of the flux follows a flux path 54 that passes through coil 72, but not coil 74. This is because, with the reciprocator all the way to its right, as shown, only those portions of the reciprocator 36 and stator 22 to the left of the slots 60, 62 and 68, 70, are aligned to provide a flux path having a narrow air gap. This path thus represents the path of lowest reluctance, and all of the flux passes therethrough, except for leakage flux.

Similarly, with the reciprocator