Abstract:
An electrostatic rotating electrical machine employs interdigitated axial pegs on opposed rotor and stator plates, the pegs immersed in a high dielectric constant fluid. Peg shape, length and positioning may be varied to tailor a changing aspect profile to a desired power source.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to rotating electrical machines (e.g., electrical motors and generators) and m particular to a rotating electrical machine employing axially extending interdigitated pegs. 
         [0002]    Electrical motors and generators share similar structures of an electrically interacting stator and rotor and may be collectively termed “rotating electrical machines,” Conventional rotating electrical machines may be roughly divided into “electromagnetic” devices exploiting magnetic fields and/or change in inductance (reluctance) between moving parts, and “electrostatic” devices exploiting electrical fields and change in capacitance between moving parts. 
         [0003]    Electrostatic rotating electrical machines have a number of advantages over conventional electromagnetic rotating electrical machines including the elimination of magnets and costly rare earth materials, significant weight from ferrous materials, and high current copper windings. 
         [0004]    Electrostatic machines are commonly found in micro-scale, micro-electromechanical systems (MEMS) which permit extremely small gaps between rotor and stator elements allowing high capacitance and high electrical fields. For larger scale rotating machines, for example, those providing integer horsepower and larger outputs (macro-scale), the physical gap between the stator and rotor may be one to three orders of magnitude larger than that for MEMS machines. This larger gap requires higher applied voltages typically in the tens or even hundreds of thousands of volts for comparable torque. These high voltages normally require ultrahigh vacuum containment vessels to prevent arcing between stator and rotor components. 
         [0005]    The simultaneous requirement of minimizing the gap (tolerances) between stator and rotor components and using high voltage driving power can present significant manufacturing challenges in manufacturing macro scale electrostatic motors. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a versatile design for macro-scale electrostatic motors that simplifies manufacture by eliminating plates in favor of interdigitated pegs immersed in a high dielectric strength, high dielectric constant fluid. The pin-style construction allows increased design flexibility through modification of peg spacing alignment and dimensions, allowing variations in capacitance as a function of rotation to be maximized and closely matched with available driving voltages/currents for improved torque and torque consistency. 
         [0007]    Specifically, in one embodiment, the present invention provides an electrostatic machine having a housing and an axle extending along an axis and supported on the housing for rotation about the axis. At least one rotor element is attached to the axle to rotate therewith and to provide a plurality of axially extending rotor pegs. At least one stator element substantially fixed with respect to the housing provides a plurality of axially extending stator pegs moving between the rotor pegs in interdigitated fashion with rotation of the rotor. A high dielectric fluid is held within the housing to surround the rotor pegs and stator pegs, the high dielectric fluid providing a breakdown voltage of at least 5,000 volts per millimeter. 
         [0008]    It is thus a feature of at least one embodiment of the invention to eliminate the need for ultrahigh vacuum containment vessels for the rotating machine such as increase the cost and size of the machine while reducing its efficiency through vacuum pump losses. 
         [0009]    The high dielectric fluid may also provide a relative permittivity of greater than five. 
         [0010]    It is thus a feature of at least one embodiment of the invention to allow relaxed tolerances in the separation between stator and rotor elements necessary for practical manufacture of macro-scale machines. The high relative permittivity provides increased capacitance between rotor and stator elements offsetting the effects of greater separation and lower field strength for a given voltage between these elements. 
         [0011]    The stator pegs may include first and second sets of concentric circular rows of pegs, where the pegs of each set are also in radial rows. The rows of the first and second sets are angularly offset with respect to each other. The pegs in each circular row are in electrical communication with other pegs of the given circular rows and isolated from pegs of other circular rows. 
         [0012]    It is thus a feature of at least one embodiment of the invention to provide a compact design that permits a rotating electric field and torque smoothing through multiphase excitation. 
         [0013]    The rows of the first set of stator pegs may be angularly positioned halfway between the rows of the second set of stator pegs and the electrostatic machine may further include an electrical power supply providing a first and second waveform to the first and second sets respectively where the first and second waveforms are substantially 180 degrees out of phase. 
         [0014]    It is thus a feature of at least one embodiment of the invention to provide an electrostatic motor with improved torque consistency that may be readily powered from a single-phase power source using transformer circuitry. 
         [0015]    The rotor pegs and stator pegs may have a substantially constant cross-sectional diameter measured in a plane perpendicular to the axis 
         [0016]    It is thus a feature of at least one embodiment of the invention to provide an electrostatic machine with a capacitance profile (change in capacitance as a function rotor angle) that reduces angular ranges of constant capacitance that result in torque dropout. 
         [0017]    The rotor pegs and stator pegs may be configured to provide a varying mutual capacitance whose derivative matches a respective of the first and second waveform providing power to the rotor and stator pegs. 
         [0018]    It is thus a feature of at least one embodiment of the invention to maximize energy transfer to the electrostatic machine by coordinating voltage and change in capacitance for maximum torque. 
         [0019]    The rotor pegs and stator pegs may be circular in cross-section. 
         [0020]    It is thus a feature of at least one embodiment of the invention to provide a readily manufactured peg shape that reduces field concentrations that could promote arcing. 
         [0021]    The pegs may be coated with a material with a high dielectric constant of greater than 10. 
         [0022]    It is thus a feature of at least one embodiment of the invention to provide an insulator that may also ensure electrical isolation between rotor and stator elements. 
         [0023]    At least one of the rotor and stator may be constructed of an insulating substrate with a conductive metal coating. 
         [0024]    It is thus a feature of at least one embodiment of the invention to permit lightweight rotor fabrication with complex shapes using techniques such as injection molding. 
         [0025]    The stator pegs may include a first, second, and third set of stator pegs in electrical communication with other pegs of a given set and isolated from pegs of other than the given set, wherein the pegs of the first, second, and third sets are arranged at angularly equal periodic spacing about the axis and further including an electrical power supply providing a first, second, and third waveform to the first, second, and third sets respectively where the first, second, third wave forms are substantially 120 degrees out of phase with each other in the manner of three-phase electrical power. 
         [0026]    It is thus a feature of at least one embodiment of the invention to permit construction of a three-phase electrostatic motor usable with common electrical power sources. 
         [0027]    Each set of rotor pegs may include clusters of multiple angularly spaced rotor pegs. 
         [0028]    It is thus a feature of at least one embodiment of the invention to present multiple angularly dispersed pegs in each phase allowing improved tailoring of the capacitance profile. 
         [0029]    The rotor pegs within a cluster have a varying axial length among different pegs of the cluster. 
         [0030]    It is thus a feature of at least one embodiment of the invention to permit control of the capacitive profile by changing an overlap between rotor and stator pegs. 
         [0031]    The electrostatic machine may further include slip rings for providing a direct electrical voltage or current to the rotor pegs. 
         [0032]    It is thus a feature of at least one embodiment of the invention to permit the enhancement of torque by the control of electrostatic charge on the rotor. 
         [0033]    These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0034]      FIG. 1  is an exploded perspective view of one embodiment of the present invention providing overlapping axial pegs extending from rotor and stator elements; 
           [0035]      FIG. 2  is a cross-section taken along line  2 - 2  of  FIG. 1  in an unexploded configuration showing overlap of the rotor and stator pegs as immersed in a high dielectric fluid; 
           [0036]      FIG. 3  is a cross-section taken along line  3 - 3  of  FIG. 2  showing overlap of the rotor and stator pegs together with a plot of a capacitance profile showing mutual capacitance between the two with rotation of the rotor and two possible driving voltages in solid and dotted lines; 
           [0037]      FIG. 4  is a figure similar to that of  FIG. 1  showing a rotor and one stator in isolation in a three-phase embodiment with isolated clusters of rotor pegs, also showing a three-phase driving voltage; 
           [0038]      FIG. 5  is a figure similar to that of  FIG. 4  showing a three-phase embodiment with a continuous angular range of rotor pegs; 
           [0039]      FIG. 6  is a top fragmentary view of overlapping rotor pegs and stator pegs of  FIG. 4  showing variation in length of rotor pegs for tailoring the capacitive profile; 
           [0040]      FIG. 7  is a simplified schematic of a power supply for the embodiment of  FIG. 3 ; 
           [0041]      FIG. 8  is a simplified representation of slip rings providing electrical voltage to the rotor of  FIG. 4  for improved torque through charge injection; 
           [0042]      FIG. 9  is a fragmentary cross-section of one rotor or stator peg taken along an axial plane showing use of a conductive coating on an insulating material; and 
           [0043]      FIG. 10  is a fragmentary elevational view of pins extending from one of the rotor or stator showing a depopulation of some pins to provide improved capacitive profile. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0044]    Referring now to  FIG. 1 , a rotating electrical machine  10  per the present invention may provide a rotor  12  mounted on an axle  14  for rotation about an axis  18 . The axle  14  may be supported at opposite ends by bearings  20  in turn held on end plates  22 . The axle  14  may pass through one end plate  22  to be attached to other rotating machinery, for example, to provide for a drive torque to that machinery in the manner of a conventional motor or to receive a driving force when the machine  10  is used as a generator. 
         [0045]    Referring also to  FIG. 2 , rotor  12  may comprise one or more rotor disks  24  extending generally perpendicularly to the axis  18  to rotate with the axle  14 . A set of concentrically arranged rotor pegs  26  in constant radius rows  33  may extend from the front and rear surfaces of the rotor disks  24  parallel to the axis  18 . Each of the rotor pegs  26  is electrically conducting and may be either insulated from other rotor pegs  26  by insulating rotor disks  24  or electrically joined by a conductive rotor disk  24 . In one embodiment the rotor pegs  26  arc circular cylinders capped with hemispherical distal ends; however, generally any shape of substantially constant axial cross-section is contemplated and other peg cross-sections may also be used, for example, those offering decreased flow resistance through a fluid. 
         [0046]    Flanking each rotor disk  24  along the axis  18  are two stator disks  30  of stators  31  also having axial stator pegs  32  extending inward toward a respective rotor disk  24  of the rotor  12 . The stator disks  30  are generally stationary with respect to the housing  23  and may have a central bore  29  allowing free passage of the axle  14  through the stator disks  30  to the bearings  20 . 
         [0047]    The stator pegs  32  are also arranged circumferentially along constant radius rows  34  fitting between the rows  33  of rotor pegs  26  so that the rotor  12  may rotate without interference between the rotor pegs  26  and stator pegs  32 . The stator pegs  32  are also electrically conductive but selectively isolated from each other by an insulating material of the stator disk  30 . In a first embodiment, alternate concentric rows  34  of stator pegs  32  are joined to either a first conductor  36 a or second conductor  36 b as will be described below. 
         [0048]    Each rotor disk  24  and the two stator disks  30  form a three-disk element that may be repeated along the axle  14  with the rotor pegs  26  and/or stator pegs  32  and interconnected for parallel or series operation. 
         [0049]    The end plates  22  may form part of a housing  23  that together provide an enclosed volume holding the rotor  12  and stator  31  and within which the rotor  12  may rotate. The housing  23  may be filled with a dielectric fluid  38  surrounding the rotor pegs  26  and stator pegs  32  to provide insulation therebetween, preventing arcing or other current flow and increasing the dielectric constant in the gaps between the rotor pegs  26  and stator pegs  32 . In one embodiment, the dielectric fluid may be Verterel® XF, a hydrocarbon fluid (C 5 H 2 F 10 ) having a dielectric constant from 7-10, a breakdown strength of 14,000 to 28,000 volts/mm, a volume resistivity (ohm-cm) of 10 9 -10 11  and a viscosity (cPs) of 0.67. Generally the present invention contemplates a breakdown strength of at least 5000 volts per millimeter and desirably greater than 10,000 volts per millimeter and the dielectric constant of at least five and desirably greater than seven and a viscosity of less than water and desirably less than 70 cPs. 
         [0050]    Referring now to  FIG. 3 , in this embodiment, the stator pegs  32  in each stator row  34 , at a given constant radius with respect to the axis  18 , may be aligned along radius lines  47  at equal angular spacing of 2α. Every other stator row  34  of stator pegs  32 , as one moves radially, may be offset in angle from the previous row by α. As noted before, every other stator row  34  connects to a different conductor  36   a  or  36   b.  The rotor pegs  26  may also be spaced in rows  33  of constant radius about axis  18  positioned approximately halfway between the rows  34 . The rotor pegs  26  may also have an equal angular spacing of 2α and are aligned along rotor lines  47 ′. 
         [0051]    Generally, as a given rotor peg  26 ′ moves in rotation past a first stator row  34   a  of stator pegs  32 , the given rotor peg  26 ′ experiences a mutual capacitance with proximate stator pegs  32  such that the total mutual capacitance between all rotor pegs  26  of a given rotor row  34  and the adjacent stator pegs  32  of stator row  34   a  (and electrically connected stator rows  34 ) provide a value C 1  that changes with rotational angle. This change in C 1  will be termed a capacitive profile and is shown by plotted waveform  42 . With the described angular spacing of rotor pegs  26  and stator pegs  32 , the periodicity of waveform  42  will be 2α with peak values of capacitance C 1  when rotor pegs  26  are aligned radially with stator pegs  32 . The torque caused by electrostatic attraction between rotor pegs  26  and stator pegs  32  of stator row  34  will be a function of a product of the rate of change of the capacitance C 1  and the square of the applied voltage to stator pegs  32 . Accordingly, a voltage waveform V 1  applied to stator pegs  32  will desirably have a nonzero magnitude (including a peak value) during the positive slope of C 1  and a low or zero magnitude during the negative slope of C 1  (where the resultant torque would be negative and hence counterproductive). A highest average torque is obtained, when the highest values in the driving voltage are aligned with the highest positive derivative of C 1 . 
         [0052]    When waveform  42  of C 1  is approximately sinusoidal and a sinusoidal driving power is used, maximum average torque is provided using a sinusoidal voltage V 1  with the phase lag of 90 degrees (α/2) with respect to waveform  42 . 
         [0053]    Insofar as sinusoidal voltages/currents may be readily obtained for motor driving, a sinusoidal capacitive profile of waveform  42  may be desirably promoted. This capacitive profile is encouraged by matching compact rotor pegs  26  and stator pegs  32  as opposed to having one set of pegs extend at substantial width along the circumferential direction such as would tend to promote a trapezoidal waveform  42  providing sections of constant capacitance C 1  such as would promote zero torque. 
         [0054]    Similarly, if capacitance profile waveform  42  were triangular, as indicated by waveform  42 ′, a square wave voltage signal V 1 ′ would provide the highest average torque. Such a square wave can be produced by solid-state switching devices gating a DC voltage/current source. 
         [0055]    Note that in both cases the alternating waveform of voltage of V 1  or V 1 ′ is given a DC offset, i.e. it is a DC value with AC component riding on it. The DC voltage provides a nonzero electrical field and induces electrostatic charge separation in the floating rotor pegs  26 . In another embodiment to be discussed below where direct electrical connection may be had by the rotor pegs  26 , this induced field is not required. The magnitude of the voltage may be reduced to zero by the AC component at certain points when negative torque would otherwise be generated. 
         [0056]    Referring still to  FIG. 3 , the present invention provides a second stator row  34   b  of stator pegs  32  staggered with respect to the first stator row  34   a  of stator pegs  32  on the rotor disk  24  and positioned to generate a peak torque when the torque produced by stator pegs  32  of first stator row  34   a  is lowest thus also providing improved torque consistency. In this case, a waveform  46  of capacitance C 2  provides a 180-degree phase relationship with respect to the waveform  42  of capacitance C 1 , and similarly a voltage V 2  with a 180 degrees phase relationship with respect to voltage V 1  may be advantageously applied to conductor  36   b  and stator pegs  32  of stator row  34   b.    
         [0057]    Referring momentarily to  FIG. 7 , a power source  48  producing the desired waveforms may employ a DC power supply  50  placed in series with two AC power supplies  52   a  and  52   b,  each of these latter AC power supplies  52   a  and  52   b  producing identical sinusoidal (square wave) output voltages with 180-degree respective phase difference. These AC power supplies  52   a  and  52   b  may be easily implemented by using two independent secondary windings of transformers having a common primary AC input and wiring the two secondaries with opposite polarity. 
         [0058]    The AC power supplies  52   a  and  52   b  may connect with conductors  36   a  and  36   b,  respectively. The return or ground side of DC power supply  50  may be held at the same potential as the rotor pegs  26 , for example, by a brush connection or the like. 
         [0059]    Referring now to  FIG. 4 , in an alternative embodiment, the rotor pegs  26  of the rotor  12  may be collected into isolated clusters, for example, angularly opposed rotor clusters  60   a  and  60   b  each spanning in this depiction approximately 60 degrees of angular range about axis  18 . In contrast, the stator pegs  32  may still provide a full angular range of 360 degrees about axis  18  but in this case are electrically connected together to form similar sized stator clusters  62 , the stator pegs  32  of each stator cluster  62  communicating with each other but isolated from adjacent stator clusters. So, for example, six stator clusters  62  may be developed each having an angular range of 60 degrees and distributed in sequence about the axis  18 . Stator clusters  62  in opposition may be electrically connected together to provide three electrically independent stator clusters  62  labeled A, B, and C. 
         [0060]    Each of these stator clusters  62  of A, B, and C may be provided with a different voltage waveform  64 a- 64 c being, for example, different phases of three-phase electrical power providing sinusoidal voltages having a 120 degrees phase difference with the other phases. It will be understood that this connection creates a rotating electrical vector about axis  18  that will apply a corresponding rotational torque to the rotor clusters  60   a  and  60   b.  In effect, as the rotor spins, a rotating capacitance wave is also created such that the capacitance rises and fall among the phases. The capacitance and voltage waves must be synchronized. The angle between the rotating waves controls the power/torque output, much as in rotating electromagnetic machinery. 
         [0061]    It will be appreciated that the stator clusters  62  need not extend a full 60 degrees as shown but, instead, may extend by as much as 120 degrees for a single stator cluster  62  with a corresponding increase in the size of rotor clusters  60  or conversely may be broken into multiple smaller stator cluster sizes, for example, of 30 degrees, 10 degrees, or even to individual stator radius lines  47 . In all cases the stator clusters  62  alternate A, B, C electrical connections. A larger number of stator clusters  62  and rotor clusters  60  will produce a slower motor speed and more uniform motor torque for a given frequency of waveforms  64 . As before, the size and numbers of the stator clusters  62  and rotor clusters  60  are matched to accomplish desired operating characteristics. More generally, the angular range of the rotor cluster  60  may be larger than the angular range of the stator cluster  62 , for example, being 90 degrees for the rotor cluster  60  and and 60 degrees for the stator clusters  62 . This allows for a transition from one phase to another that provides an improved capacitance profile. 
         [0062]    Referring now to  FIG. 6 , the rotor pegs  26  of each rotor cluster  60  may be given different axial lengths to modify the capacitive profile exhibited as the cluster  60  moves through the stator pegs  32  of a given cluster  62 . This modification of the rotor pegs  26  may be done to better match the capacitive profile to the driving waveform, for example, to make it more sinusoidal or more triangular. Alternatively, or in addition, the same modification could be done with the stator pegs  26 . 
         [0063]    Referring now to  FIG. 10 , the pegs  26  or  32  of either the rotor  12  or stator  31  may further have their length essentially reduced to zero to modify the capacitive profile exhibited between clusters  60  or  62  as they pass each other. In this case, pegs  26  or  32  at the peripheral outer edges of radial lines  47  at the leading and trailing side of the clusters  60  and  62  are progressively remove removed as one moves away from a center of the cluster to smooth a trapezoidal capacitive profile waveform  80  between clusters  60  and  62  to a more sinusoidal capacitive waveform  80 . This technique which emphasizes not only length but location may be combined with a nonzero varying lengths of pegs  26  or  32   
         [0064]    Although the rotor pegs  26  of the rotor clusters  60  may be electrically floating on an insulating rotor disk  24 , in one embodiment slip rings  70  may be provided so that a DC bias from a DC power source  72  may be applied across, for example, opposite rotor clusters  60   a  and  60   b  providing them with a net charge that will be attracted to opposite charges applied to the stator clusters  62 . In this case the opposite stator clusters  62  may also be given different polarities, for example, by providing waveform  64   a  to a first stator cluster  62  and having waveform  64   a ′ be 180 degrees out of phase with waveform  64   a  to an opposite stator cluster  62 . This ability to provide for repulsive as well as attractive forces between rotor pegs  26  and stator pegs  32  raises the possibility of bipolar operation with appropriate phasing of the clusters  62 . 
         [0065]    Referring now to  FIG. 9 , each of the rotor pegs  26  and stator pegs  32  need not be fully conductive but only require an outer conductive surface that can support the necessary electrical charge. Accordingly, the rotor pegs  26  and stator pegs  32  may be, for example, constructed of injection-molded thermoplastic being electrically insulating and having a high electrical breakdown. This insulating core may be coated with a conductive layer  71 , for example, by sputtering or electroplating with a conductive metal such as copper, aluminum, or nickel. The conductive layer  71  may be in turn coated with an insulating material  73  which may also provide a high dielectric constant. Examples of such include titanium dioxide (TiO 2 ) having a dielectric constant ε r  of greater than 80 or barium titanate (BaTiO 3 ) having a dielectric constant ε r  of greater than 1500. Electrode materials may also be incorporated into the rotor pegs  26  and stator pegs  32 . 
         [0066]    The dielectric fluid  38  may include ferroelectric particles for enhanced permittivity. 
         [0067]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0068]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0069]    It will be generally understood that the electrical machines described herein may be operated either as motors or generators and in the latter case that the tailoring of the capacitive profile may be done to provide a desired output waveform. 
         [0070]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.