GB2455113A

GB2455113A - Electromagnetic machines having windings formed of laminated conductors.

Info

Publication number: GB2455113A
Application number: GB0723349A
Authority: GB
Inventors: Phillip Raymond Michael Denne
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-11-29
Filing date: 2007-11-29
Publication date: 2009-06-03
Also published as: GB2455113A8; GB0723349D0

Abstract

An electromagnetic machine comprises relatively moving first 2,3,4,8 and second part 28. The first part consisting of an extending array of oppositely polarised paired magnetic pole means 2,3 (pms, electromagnets or passive windings) and mounting beams 4 and 8, the pairs of pole means defining an air gap (linear or annular) there between and the second part comprising a conductor assembly 1,5,7 located in the air gap between the facing pole means embedded in cap beams 9 supported by bearings 6, the assembly being formed as regular conductive path patterns 13,20 within at least one apertured lamina of conductive material having no substrate by cutting along lines 21. Patterns 15,16 may be superimposed to form a winding structure with terminals 17, 18, three sets of this structure forming the phase conductors 1,5,7 (see also figs 6-9). The machine may be linear as shown in fig 1 or as shown in figs 12,15 rotary, having the conductors and magnetic pole arrays concentric or radial with respect to the machine axis. Alternatively the paired magnetic arrays may be replace by a single array 3 opposing an iron plate 32 or if the assembly comprises an induction machine, by opposed arrays of passive conductors. The arrangement may be used in gas struts and the second part may form a continuous loop track on which a number of sets of independent magnetic assemblies can be mounted which can be applied to overhead cranes or elevator systems. The linear embodiments may have the elements in the form of a circle or polygon array so as to balance magnetic forces (Fig 16-18). The invention relates especially to the design of high-thrust linear and gearless rotary electromagnetic machines using high-density magnetic fields. By the use of this invention, large machines may be built from a concatenation of lightweight elemental components in which there are no copper wires the function of the wires being performed by conducting paths within the monolithic laminae.

Description

1 2455113 Improvements in electrical machines The present invention relates to the design of linear electric motors and to high-torque rotary motors. Many electrical machines are designed to produce a force by the mutual interaction of magnetic field patterns in both the armature and the stator, at least one of the magnetic field patterns being electrically varied. In what follows, however, we describe (hitherto less common) electromagnetic machines having distinct electrical and magnetic parts. In such machines the motor force is not "inter-magnetic" but results from the action of the magnetic fields of one part upon moving electrical charges in the conductors of the second part. It will also be understood that when driven as a generator, relative motion of the parts causes current to flow in the machine conductors.

It might be thought that the distinction is purely academic and that the modus operandi of any electrical machine might be described either way.

That is not the case and it is important to recognise that machines that are designed to operate by the mutual interaction of magnetic fields may be physically distinguished from those that are designed to operate electromagnetically.

"Inter-magnetic" machines are so constructed that the area enclosed by a looped conductor (or an equivalent bundle of conductors) is matched to that of the magnetic pole pieces, or is a coarse fraction thereof. In contrast, in an electromagnetic machine, the area dimensions of the electrical conductors (or bundle of elemental conductors) themselves match those of the magnetic pole pieces -or are a coarse fraction thereof.

As a further distinction, in "inter-magnetic" maclimes the frontal area of the coil is relatively small. The coil often encloses a volume of high-permeability magnetic material whose function is to increase the effective flux density of the electromagnet and to reduce the air gap distance of the magnetic circuit. To make the coils surround the iron, the coils of an "inter-magnetic" machine are usually placed in slots Cut into the iron -the coils themselves are not in the air gap and the air gap distance is small.

in contrast, in electromagnetic machines the electrical conductors are designed to have a large frontal area and they are usually placed directly in the (larger) air gap between the magnetic pole pieces and the high-permeability magnetic material or "backing iron". It is not necessary (although it may sometimes be convenient) for the conductors of an electromagnetic machine to form complete loops or coils it is known to construct linear electric motors in cylindrical form in which the output is a rod or tube, or in planar form in which the armature moves upon the surface of the stator or in a channel between two similar stators.

It is also known to construct such machines with an armature that is not connected externally but used as a piston for compression, for controlled expansion (the motor being driven in reverse and acting as a generator) or as an inertial mass, the reaction forces being coupled to the load via the stator.

In either topology, the magnetic part generally consists in an array of permanent magnets that produces a spatially-periodic magnetic field transverse the locus of relative motion. The electrical part of a linear motor consists in at least one array of coils or electrical conductors intersecting the said spatially-periodic magnetic field in a direction orthogonal to both the locus of motion and to the magnetic field.

In many forms of electric motor of conventional construction, the electrical part of the machine consists in coils of wire that are wound in slots of an iron structure. The iron structure holds the coils in position and provides the mechanical strength necessary to transfer the electromagnetic forces on the wires to the body of the machine -and it also serves as a path of low reluctance for the magnetic flux. That is to say, in a conventional electric motor the electrical conductors are effectively immersed in the iron. An important result of using that topology is that the effective flux density experienced by the wire is limited by the practical geometry of the slots in the iron structure and by the permeability of the iron, so that the wire behaves as though it intersects a magnetic field whose working flux density is generally in the order of 0.6 Tesla.

It is desirable to operate an electromagnetic machine with a high flux density in the region of the coils, so as to reduce the current required for any given output force or torque. That is because the force P (in Newtons) produced by an electromagnetic machine is the vector cross product of the magnetic field strength B (in Tesla), the length of the electrical current path L (in metres) and the strength of that current I (in Amperes). Further, since the resistive heat loss (commonly called "copper loss") increases with the square of the current, it is especially desirable to use a high working flux density in machines that are required to produce a high-thrust output, so as to minimise the copper loss.

In this document we describe means by which the magnetic flux density in which the conductors are immersed may be increased to around 1.5 Tesla, at which point it begins to be limited by the saturation of readily-available magnetic materials such as mild steel. (By the use of special magnetic materials the field strength may be further increased, but not to more than about 2 Tesla at this time) The increased magnetic field strength has the disadvantage that it causes larger internal forces within the machine, because the force F (Newtons) between two plane magnetic surfaces having an area A (sq m) and linked by magnetic flux having a density B (Tesla) increases with the square of the flux density linking those surfaces and is given approximately by F 400,000 B2A That is to say, the field produces an effective "magnetic pressure" forcing the two surfaces together, whose value in Bar is equal to 4B2 For example, if a flux density of 1.5 Tesla emerges from a pole piece 5 mm wide and 100 mm long, the pole piece is constantly attracted to an adjacent flux-return plate by a force of 450 Newtons. A typical armature with 50 such pole pieces will produce a large magnetostatic force of 22, 500 Newtons. If the electrical efficiency of the machine is improved by the use of special magnetic materials and the flux density is increased to 2 Tesla, the magnetostatic force produced by an armature of the same size will increase to 40,000 Newtons.

Many conventional linear motors are designed in such a way that they consist in an armature with a stator on one side only, the armature being held clear of the stator by a bearing system. Any proposed increase in flux density between the two parts is discouraged because the full magnetostatic force has to be resisted by the armature bearings.

The topology of an industrial linear motor is often modified so that the electrical armature travels along the centre line of a parallel-sided channel lined with magnets, so that it experiences approximately equal forces of attraction to the opposite sides of the stator channel. Nevertheless, it will be understood that any imbalance between those opposing forces will have to be resisted by the bearings that centralise the armature position. As the flux density is increased, the magnitude of those opposing forces increases rapidly and the effect of any imbalance is also greater. Thus the armature bearings of a conventional linear motor must he made more robust if the flux density is to be increased.

The characteristics of even the best available magnetic materials are such that the optimum working flux density at the surface of a permanent magnet (the condition of BH maximum) is only a fraction of a Tesla. Thus, if the flux density in the gap between the armature and the stator is to be increased to more than one Tesla, it is necessary to use pole pieces that concentrate the flux from the magnet surface into a much smaller area.

The flux density is then multiplied by the area ratio, providing that the pole piece material does not saturate magnetically.

In our previous inventions relating to cylindrical machines, the magnets are plane flat discs magnetised between parallel surfaces. In such designs, an iron pole piece of similar form is fitted on either side of the magnet, so that the pole pieces are the "bread" of a circular sandwich with the magnet in the middle, which together might be called a "force unit". The function of the pole pieces is to concentrate the flux from the plane faces of the magnet and to divert it radially so that it emerges from the cylindrical periphery of the pole pieces.

In the machines of this invention, the magnets and pole pieces are flat plates and the flux is arranged to emerge (at increased concentration) from two opposite planar sides. In three-phase machines the pole pieces and the magnets have the same thickness -and that dimension is also the spacing between the coils along the axis of motion. So if it is necessary to decrease the axial thickness of the pole piece so as to further concentrate the flux, the magnet thickness and the dimensions of the electrical conductors must also decrease. Thus a machine having a high flux density has more magnetic poles (of alternating polarity) per unit length of its line of motion. For any given speed of travel of the armature relative to the stator, the frequency of flux alternations increases with design flux density.

Iron associated with the electrical conductors is commonly called "backing iron" and the amplitude and direction of the magnetic flux in the iron alternates as the armature moves relative to the stator. 1'hat alternation of field direction causes energy to be dissipated in the iron -and the "iron loss" increases as the square of the flux density.

For all of the above reasons, electrical machines of high working flux density are not commonly available and they are restricted to specialist applications for which the corresponding disadvantages can be accepted.

It is an object of this invention to provide an economical means of constructing an electrical machine in which the electrical conductors are placed in a high-flux density magnetic field, thus minimising the "copper loss".

It is a further object of this invention to eliminate entirely the backing iron of the electrical conductors so that the "iron loss" is reduced to zero.

It is a further object of this invention to eliminate magnetic attraction between the armature and the stator, reducing bearing wear and making assembly safer and less costly It is a further object of this invention to minimise the mass of a moving electrical armature so as to increase the operating bandwidth of the machine.

It is a further object of this invention to incorporate the above-listed inventions into a basic linear motor element having a range of topologies.

It is a further object of this invention to show means by which many such motor elements may be combined to form a range of compact high-power electrical machines, both linear and rotary.

In this invention an elemental electromagnetic machine is comprised of two parts, the armature and the stator, the armature being arranged to move along or parallel to an axis of symmetry of the stator, the first part being constructed of planar magnets having a chosen thickness and of pole pieces having a thickness related thereto, the pole pieces being arranged to produce a high-density magnetic field transverse the electrical conductors of the machine, the said field being of regular alternating polarity and with a regular spatial period, the second part being constructed from a series of electrical conductors having surface area dimensions substantially equal to or a coarse fraction of the area dimensions of the pole pieces of the first part, the conductors thus intersecting the transverse magnetic fields of the first part and current being arranged to flow in the conductors so that there is produced by the interaction of the electrical currents and the magnetic field an electromagnetic force whose magnitude and sign may be controlled by the said electrical currents, the arrays of conductors of the second part being constructed from a plurality of monolithic patterned metal laminations having no substrate and being bonded together to form a self-supporting structure.

In this invention there are no wire coils and such machines may be referred-to as wireless motors. The electric currents instead flow in two-dimensional electrical conductors, which are not immersed in an iron flux conductor but are positioned in a magnetic field of high flux density. The electrical machines herein described are therefore exceptionally efficient and they are capable of producing large forces and of operating at high power levels.

It is known to use patterned metal laminations in place of wound coils in rotary electrical machines, one example of which is taught by US 4,319,152, which in turn refers to the Dutch Patent Application 670 6453. In the US document it is further conjectured, without example, that such structures might also be employed in linear motors. It is to be noted that in the prior art the use of laminar conductors has been conceived to be only for the energisation of electromagnets and as a simple and direct replacement for wire that could have been used for the same function. It is also to be noted that Figure 3 of that document shows two forms of a slotted iron or ferrite core, into which the metal laminations are intended to be placed -there is no intention that the backing iron is to be eliminated, nor that the laminated conductors shall be self-supporting.

We refer also to GB1420391A, which describes the construction of a robust coil system to produce magnetic fields for the levitation of specialised railway vehicles. By the use of at least one other set of coils, the magnetic fields can be commutated so as to produce a differential force causing forward motion of the railway vehicles. It is clear from the design constraints described therein that the currents must be very large and so the conductors must perforce be busbars of convenient rectangular section. It is to be noted that the busbars are simply bent to the required shape and that they are not constructed from a stack of laminations having the required current paths defined by previous patterning. It is to be further noted that the dimensions of the conductors are not matched to those of the pole pieces of the magnetic part (affixed the vehicle), nor are they nested so as to reduce the magnetic air gap distance.

We now refer to JP62189931A, which describes a number of methods of constructing an electrical component of a rotary motor using a ribbon conductor. The inventor teaches that such fabrication would be possible by applying a complex series of contortions to a single conducting ribbon.

He also says that the number of turns could be increased if necessary by using in place of the conducting ribbon a component that might be termed "ribbon cable" -a number of wircs laid and bondcd side by side to form a flat cable. It is not conceived by JP62189931A that the electrical component might be formed from patterns punched from one lamination, or that the number of turns might be increased by stacking a number of such preformed laminae.

From study of these and other prior art, it will be clear that it has not been in the mind of any previous inventor to interdigitate and bond a plurality of laminar phase conductors so as to form a complex and robust mechanical structure, intercepting a periodic magnetic field of high flux density as part of a brushless servomotor, whether linear or rotary. Nor does the prior art describe a concatenation of many such elemental machines so as to produce a compact and powerful motor of exceptional performance.

It is known to use a stack of circular flat disc permanent magnets and pole pieces to construct an axially-alternating magnetic field having a high radial flux density. However, such cylindrical prior art structures are strongly limited as to the maximum axial force that they are capable of prod udng continuously because: - 1. The thrust of the magnetic piston is proportional to its volume or mass -directly to its length and to the square of its diameter.

2. There is, in any application, a practical limit to the piston length of a cylindrical actuator and it is therefore necessary to increase the disc diameter if greater thrust is required in a limited space. But there is also a limit to the maximum diameter of a one-piece magnet disc that is set by the practical difficulties of its manufacture as a pressed and sintered component.

3. There is a similar limit to the volume of a one-piece magnet that is set by the power required for its energisation by a pulsed magnetic

field.

4. As the unit size of a powerful permanent magnet is increased, it becomes more dangerous to handle during the process of building the motor.

5. If it is essential to use a large-diameter disc magnet, there is no alternative but to assemble the large circular disc from many smaller segmental magnets, which must first be magnetised and then brought together (against strong mutual repulsion) before being bonded to an iron pole piece. Such an assembly process is both difficult and dangerous.

6. The magnetic remanence is decreased along the line of each junction between the segments (an effect called "fringing") so that a smaller amount of magnetic flux is available from an assembled magnet than from the equivalent one-piece component.

7. In a cylindrical linear actuator of conventional construction all the coils forming the phase windings must be constructed individually, assembled as a stack and wired together with the correct phasing, then bonded to each other, to an internal lining that forms the bearing surface for the piston and finally to the thick outer casing that forms the backing iron of the machine. That manufacturing process is labour-intensive, its quality is difficult to control and it is costly.

Nevertheless, there is a demand for larger and more powerful cylindrical linear actuators than those that can be constructed according to the prior art. For that reason we have developed a range of high-power electrical machines that are efficient, low in cost and safe to manufacture. The novel motors are assembled from a number of elemental machines, whose construction and operating principles we now describe with reference to the attached diagrams. It will be understood that the machines illustrated herein are by way of example and that the scope of our invention is not limited thereto.

Figure 1 shows in diagrammatic form a lateral cross section of an elemental linear actuator, constructed in accordance with the principles of this invention.

The electrical conductor vane 28 and the magnetic field system 2, 3 move relative to one another along the machine axis, which is perpendicular to the sectional diagram. The electrical conductor vane 28 intercepts the strong axially-periodic magnetic field that passes between the complementary magnetic systems 2 and 3 that are arranged to lie close to and on either side of it. The magnetic field systems are in this arrangement affixed the non-magnetic side plates 4. Because the north poles of the periodic magnetic array 2 are arranged to be opposite the south poles of the magnetic array 3 and vice-versa, it will be understood that there are large magnetostatic forces between the side plates 4 to which the arrays are affixed, so that the top and bottom plates 8 are necessary to maintain an accurate spacing between the robust plates 4.

The conductor vane 28 is comprised of three sets of conductors 1, 5 and 7, which are interlaced in the central region between the magnetic systems 2 and 3 but their interconnecting parts or "end windings" overlap at the edges.

In this arrangement the edges of the conductor sheets are embedded in cap beams 9. If the electrical part of the machine is considered to be fixed (i.e. to be the stator) the cross beams 8 support bearings 6 that allow the magnetic armature assembly to travel along the electrical stator vane without touching it. Conversely, if the electrical part is considered to be the armature, it moves between the magnetic arrays 2 and 3 along the bearings 6.

It will be noted that there are no magnetic materials in the electrical part of the machine and there are therefore no magnetostatic forces that draw the conductor vane 28 towards either magnetic system 2 or 3. The bearings 6 are therefore lightly loaded.

Figure 2 is a diagrammatic longitudinal cross section of a part of the motor shown in the previous figure. The numbers refer to the same components as indicated for Figure 1, although the scaling of the diagram is different to aid clarification. Each of the magnetic arrays 2 and 3 is composed of magnets 10 producing a flux parallel to the axis of motion that is turned through a right angle and concentrated by pole pieces 11 to cross the electrical conductors 1, 5, 7 that are disposed along the central axis. The flux from each magnet is therefore linked with that of an opposite magnet of complementary polarity. Whilst the pole pieces 11 are made from iron or other convenient high-permeability material, the volumes 12 are low permeability regions of air, dielectric or a non-magnelic metal such as aluminium. It will be understood that shaping the pole pieces in this way strongly discourages flux leakage outwards through the plates 4.

It should be noted that the electrical conductors of the three phases 1, 5, 7 are interdigitated in a repetitive sequence along the axis of motion of the machine.

Figure 3A is a diagrammatic representation of one laminar electrical conductor, showing how it can be punched from a wide strip of (e.g.) aluminium. In this diagram the dashed lines 21 show the side cuts after punching. The width of the transverse conducting paths 13 (which is marginally less than that of the magnets 10 and the pole pieces 11 referred-to in the previous figure) is less than half the width of gap 14. It will be understood that the surfaces of the lamination are coated with insulating material and that the width of the axial conducting paths 20 may be conveniently greater than the width of the transverse conducting paths 13 so as to reduce their resistance and improve machine efficiency. Figure 3B is a simplified representation of the finished lamination to which we refer in later parts of this document.

Figure 4 is a diagrammatic representation of two identical laminar electrical conductors of the kind illustrated in Figure 3, one being reversed with respect to the other and having connection tags 17 and 18 at their lower ends. If the laminations are made of aluminium, the necessary surface insulation may be conveniently formed by a hard anodising process.

Figure 5 shows diagrammatically the two laminations of Figure 4 laid and bonded precisely one upon the other and having the end transverse paths or "tines" 15 and 16 welded together to form a high-quality electrical connection. It will be understood that there is now a continuous electrical path between the two connection tags 17 and 18, by which current may be caused to flow along the series-connected laminations, passing always in the same direction through each transverse conducting path or tine. It will also be noted that, whilst the original punched laminar conductor is mechanically weak, the layers when bonded together produce a strong metal vane that may also be considered to be a concatenation of many electrical coils. It will be understood that the technique of reversing alternate conducting layers may be extended to the use of many layers, so as to achieve any

desired performance specification.

Figure 6 is a diagrammatic representation of three sets of laminar conductors of the form shown in Figure 5. The sets of conductors correspond to the phases 1, 5 and 7 according to the previous figures and it will be seen that the thrust-producing conductors in the high-density magnetic field (the tines) are interdigitated with one another in the central region and that they overlap one another at their outer edges, where the current path is in an axial direction. The edges 20 of the laminar conductors therefore correspond with the end windings of a conventional motor.

Figure 7 is a further diagrammatic illustration of the technique by which the three sets of laminations, corresponding to the three electrical phases 1, 5 and 7, may be interdigitated and bonded together to form a strong mechanical structure of precisely-defined dimensions. It is a view of Figure 6, looking along the length of the laminations and it shows how the three phases are nested together in the central region and overlap at the edges 20.

By way of illustration of the generality of the construction principle, we here show each phase conductor system as consisting of four layers; but it will be understood that it may be only one layer or many layers, depending on the

motor design specification.

Figure 8 is a diagrammatic view of the assembly of Figure 7 after compression and bonding in a production jig. It should be noted that although the electrical vane is narrow in the central region, it is rigid in flexure.

Figure 9 shows in diagrammatic form how the conducting vane is precisely fitted into at least one cap beam 9. The cap beam or beams 9 are the means by which the electromagnetic forces generated in the vane are transferred to the body of the motor or by which they are transferred to the load. The cap beam(s) provide extra longitudinal stiffness to the electrical vane and they are also the means whereby heat generated in the body of the vane is conducted away from the plates of the end windings. Coolant channels 31 are shown as one means by which the resistive heat can be conveyed from the conducting vane by the cap beam 9.

We now show how the elemental machine described above may be used to construct wireless electrical machines having a variety of topologies, in the following diagrams, by way of example and without limitation, we have chosen to concentrate on a brushless three-phase permanent magnet configuration. Nevertheless, by application of the same principles it is also possible to design wireless electrical machines of any other configuration.

Figure 10 shows a diagrammatic sectional plan view of a linear motor of the type shown in Figure 1 in which the magnetic system 4 is the armature and travels on bearing(s) affixed the cap beam(s) of the electrical stator 1, 5, 7.

it will be understood that the position of the armature and its relationship to the individual phase conductors of the stator is measured by a position transducer (not shown) and that the power to the individual phases 1,5,7 of the motor may be controlled by any standard industrial electronic drive unit for a brushless three-phase motor.

There is no inherent limitation to the length of the stator vane, which may be divided into electrical sections so that power is only fed to that part of the stator vane adjacent the armature at any time. The centre line of the stator vane does not need to be rectilinear but that it may follow any smooth curve that does not cause the armature to collide with the stator at any point. Especially unique to such an elemental machine is that, subject to proper clearance between itself and the armature, the centre line of the wireless stator vane may follow a smooth path in three dimensions simultaneously. Further, the plane of the stator (and thus of the armature) may also be arranged to rotate smoothly around its own axis as it proceeds.

It will be understood that, to increase the ability of the armature to follow the curving path of the stator, the armature may need to include articulations or incorporate flexible materials, for example.

Figure ii shows in diagrammatic form how that such a stator sectioning technique allows several armatures 22 to be controlled independently in track sectors 33 through 38, so that they may move simultaneously back and forth along the same stator, within limits that prevent collisions. By way of example the stator track 33 through 38 is shown as a ioop, perhaps surrounding a processing centre of a manufacturing facility. in this arrangement each track segment 33 through 38 has its own electronic drive (not shown) and each armature 22 has its own position transducer (not shown) that communicates with the electronic drive appropriate to the position of the armature at that time. It will be understood that the same control principle can be applied, for example, to several overhead cranes moving on the same rail system or to several elevator cars moving in the same shaft.

Figure 12 shows in diagrammatic form how a high torque rotary machine may be formed from the elemental machine of Figure 1 by arranging for the electrical vane to follow a circular path and by extending the length of the magnetic system so as to completely enclose the electrical vane. It will be understood that the stator may be the magnetic part and the armature may be the electrical part without change of this principle. In this diagram the numbers refer to the same motor parts as in previous figures. The electrical vane, comprising phase conductors 1,5 and 7, is formed in a circle and is mounted to the lower part of the motor 25 whilst the magnetic arrays 2 and 3 are also formed in a circle and mounted via cylindrical plates 4 to the upper part of the motor 24, which rotates relative to the lower part by means of bearing and seal units 6.

Figure 13 shows an alternative arrangement by which the elemental wireless machine of Figure 1 may be configured as a high-torque rotary device. In this configuration the conducting vane 28 is assembled from laminations that are each in the form of a disc, so that the tines are disposed radially.

Again, it is possible for the machine to exist in complementary form, so that the magnetic part is fixed and the electrical part rotates. In this diagram the electrical vane 28 transfers its force (torque) to an armature shaft assembly 25, whilst thc magnet arrays 2, 3 arc affixed the casing 24.

The configuration described above may at first appear to he similar to that of a printed circuit motor, but it should be noted that the armature laminations 1. are not printed but are wholly self- supporting and without any substrate 2. have conductors that are not configured as coils surrounding iron pole pieces but have surface areas that are matched to those of the magnetic poles with which they interact 3. are interdigitated in the magnetic field region and overlaid elsewhere 4. arc dcsigned to carry much larger currents than would be possible in a printed form 5. move in a higher-density magnetic flux than is commonly employed for printed circuit motors 6. are those of a three-phase servomotor and not a DC machine It will be understood; therefore, that the configuration shown in Figure 13 is not an obvious extension of, nor is it derived in any way from, the prior art of a printed circuit motor.

The distinction will become clearer as we now consider the special advantages of the elemental wireless motor when it is necessary for the electromagnetic force (thrust or torque) to be uncommonly large.

The thrust of any wireless machine may be increased by using larger conducting vanes and larger planar magnets. However, the size increase soon encounters the same magnet size limitation that was previously mentioned in connection with the earlier cylindrical linear actuators. It is extremely difficult both to manufacture and to magnetise a Neodymium Iron Boron magnet having an area greater than about 0.01 5sq m (say 150 mm by 100 mm).

But because the elemental wireless machine of Figure 1 is narrow in cross-section, it is possible to stack a number of motor elements closely together in a small space. There is a further advantage in so doing, as we explain in the following sections.

Figure 14A is a diagrammatic cross section of a number of motor elements 30, each being similar in structure to that shown in Figure 1, but now stacked closely together. It will be understood that it is possible to connect the stator vanes 26 together mechanically and electrically -and to drive them from the same electronic unit. It will also be understood that the armatures 28 may also be coupled so that the thrust produced by any one elemental machine is multiplied by the number of machines that are acting together.

Figure 14B shows how it is possible to simplify the structure of the concatenation and to achieve a more convenient and economical dose packing. It should be noted that the magnetic arrays 26 are made common to the electrical vanes on either side of them. Thus, although there are strong magnetostatic forces between the adjacent magnet and pole piece assemblies 26, in this arrangement those forces are generally equal and opposite. For that reason the intermediate frameworks can be eliminated and the magnetic arrays may be held only by robust supports 27. All of the conducting vanes are fitted precisely into a common frame 25, which is fitted with bearings 6 so that it may move relative to the framework of the magnetic field system 24. It also becomes possible to bring the electrical vanes 28 cicar of the magnetic parts without danger of the magnetostatic forces closing the slots through which the vanes must pass. Only the ends of the magnetic framework 4 experience unbalanced magnetostatic forces and they must therefore be of robust construction Figure 15 is a diagrammatic cross section of a very high torque rotary motor using the principle of concatenation of wireless motor elements previously described. Several motors of the type shown in Figure 13 are combined to drive the same shaft and the intermediate structure is simplified in the same way as for the elemental linear motors of Figure 14.

In this example the wireless electrical vanes 28 take the form of punched discs that are interdigitated and bonded to form a self-supporting structure in the manner previously described for rectilinear laminations. The electrical conducting discs are embedded in and keyed to a central shaft 25 that runs in bearings 6. The magnet and pole piece arrays 26 are also in the form of rings that are affixed the casing 24 by locating rings 27.

It will be understood that although in this illustration only four stacked rotary motor elements are shown, there is no inherent limitation to the number of rotary elements that may be employed to produce a very high torque rotary machine.

It will also be understood that the motor illustrated in Figure 15 is a moving conductor machine, having the great advantage of low rotor inertia and a high rotor torque. Nevertheless, in some applications it may be advantageous to build an equivalent machine in which the electrical system is the stator and the magnetic system is the rotor.

The magnetostatic forces between the magnet arrays 26 are balanced in the central region and significant unbalanced magnetostatic forces only exist between the end plates 24 and the adjacent locating rings 27.

Figure 16 shows how, in the case of linear motors, such end forces may be completely removed and the magnetostatic forces balanced throughout the system. This is achieved by closing the stack of elemental motors on itself to form a circular or polygonal array having an even number of such elements disposed therein. By such means it is possible to produce a compact and highly-efficient linear actuator having a thrust more than an order of magnitude greater than the thrust of any individual motor element.

By way of example Figure 16 shows a 32-element circular array in which the elements are of the same form as shown in Figure 1. The electrical vanes 28 are affixed the outer casing 25 and alternate with the magnetic arrays 26 which arc affixed the armature thrust tube 24. Currents flowing in the radially-disposed vanes 28 cause the magnet arrays (and thus the thrust tube) to experience an electromagnetic force into or out of the plane of the diagram.

Figure 17 is an illustration of a typical armature or magnetic assembly in which the reference numbers are as before. It will be understood that in alternate slots around the armature the directions of the magnetic fields are reversed and all the mechanical forces are balanced.

Although the magnetic armature is large, it is assembled from small magnets and pole pieces ("force units'D that are brought in one at a time and laid in a circle, each strongly attracting its neighbours laterally and (much less strongly) repeffing its neighbours vertically. The magnetic armature is constructed (in a special jig) by placing the force units side by side as a series of tiles. When one circular layer is complete, the next layer built upon it, one force unit at a time. The design thus overcomes the principal scaling limitations of earlier cylindrical electromagnetic actuators and it allows a massive and powerful armature to be assembled safely.

Figure 18 is an illustration of part of an electrical machine constructed according to this invention, in which it will be seen that the electrical vanes 28 are fitted via cap beams 9 to the framework 25 and that they pass through slots in the periodic magnet arrays 2, 3.

Figure 19 is a diagrammatic representation of an alternative form of the elemental machine of Figure 1, in which the spatially- periodic array of paired magnets is replaced by only one spatially-periodic array, facing an iron plate 32 on the opposite side of the air gap. It will be understood that the iron is induced to form a spatially periodic array of magnetic poles of complementary polarity, so that the conductors continue to be placed in a transverse spatially-periodic field. The construction is simpler in form, but because the air gap is only half as wide for the same size magnets, the motor is less powerful and the power-to-weight ratio is reduced. Nevertheless, the construction might be advantageous for some applications. An elemental motor of the type shown in Figure 19 could be used to replace the elemental motor of Figure 1 in any of our concatenated motor systems, although the performance would be reduced thereby.

Figure 20 is a further diagrammatic representation of the alternative design, being equivalent to that of Figure 2, with the same nomenclature for its components. Again, the iron plate 32 replaces one of the paired axially-periodic magnet arrays and creates induced magnetic poles of complementary polarity.

It will be understood that the principles of this invention may be extended to include machines that use electromagnets in place of the permanent magnets previously considered.

It may also be extended to include induction machines wherein the array of permanent magnets is replaced by a passive arrangement of patterned conductive laminations. In such induction machines a travelling magnetic field is produced by phased alternating currents in the powered conductors and eddy currents are deliberately arranged to flow in the passive conductor array. The interaction of the induced currents and the controlled alternating currents produces an axial force. Although the resulting axial force is smaller than that produced by a machine using permanent magnetic fields or using fields produced by electromagnets, an induction machine is low in cost and light in weight and it may offer a significant advantage in some circumstances.

It will also be understood that the principles of our invention may be extended to include a concatenation of wireless linear machines of any alternative design that have parallel force vectors in a manner equivalent to that shown in Figure 14, so as to increase the force per unit length of actuator and to share common structural members so as to reduce cost and weight.

It will be further understood that the principles of the invention may be extended to include conducting vanes consisting wholly or in part of any ferromagnetic material such as iron or steel, in that case there will be a strong magnetostatic force between the armature and the stator and the machine losses will be greater than those for a machine with (e.g) aluminium conductors. Nevertheless, there may be a significant benefit because the laminated structure combines electrical and magnetic functions and the reluctance of the air gap will be considerably reduced, so that less magnetic material will be needed for the construction of the periodic arrays 26.

The pnnciples of the invention may be further extended to include a conducting material that consists in or is coated with a layer of superconducting material, with the advantage that resistive losses may be entirely eliminated and that much higher current densities can be used to produce a large force in a small space.

The principal advantages of our invention include the following: - 1. The mass of the electrical part of any electrical machine may be reduced by the replacement of copper wire by patterned laminar aluminium conductors.

2. The manufactunng cost may be reduced by shaping the cross section of the patterned conductor laminations and bonding them into a robust, self-supporting mechanical structure.

3. The insulation of the aluminium conductors by an anodising process is simple and provides a robust insulating coating that will withstand high temperature operation if necessaly.

4. The mass of the machine may be further reduced by the elimination of backing iron for the electrical conductors, which also eliminates the "iron loss" 5. Because the conductor assembly is lightweight, robust and dimensionally stable, it may, in some applications, be used as an armature of exceptionally-low inertia, thus increasing the operating bandwidth in control applications.

6. Although the magnetic field strengths are high, there is no magnetostatic attraction between the armature and the stator. This makes the machine easier and safer to assemble and it reduces bearing forces and bearing wear.

7. The same technique allows the electrical system to be manufactured and transported in sections, so that a large motor may be assembled on site without undue difficulty.

8. The electrical system of the motor is less costly than any copper wire equivalent and it may sometimes be advantageous for a long-travel linear motor to use an electrical stator.

9. A long (perhaps circuitous) electrical stator may then be built from isolated sections that are powered independently, so that several permanent magnet armatures may be moved precisely and independently on the same stator.

10. Because the elemental machine is planar in form, the locus of motion of a linear machine may follow any smooth path in three dimensions, whilst rotating on its own axis if required.

ii. A high-torque rotary motor can be constructed in disc or drum topology by using a circular electrical vane, moving between or relative to paired periodic arrays of magnetic poles.

12. A number of elemental linear electric motors may be concatenated to form a larger machine, in which process the construction of the elemental motors may be simplified to reduce size, weight and cost and to balance the internal magnetostatic forces.

13. In the same way a number of elemental rotary motors may be combined to form a rotary motor of exceptional torque, in which process the internal structure can also be simplified to reduce size, weight and cost.

14. If the concatenation of elemental linear motors forms a complete circle, the end effects are eliminated and the magnetostatic forces are balanced throughout the structure.

15. Using the aforementioned technique, a number of elemental linear motors can be housed within a compact cylindrical volume, the exceptionally-large output thrust being conveyed via a rod or tube 16. The rod or tube output of such a machine may be sealed to act as the * output element of a gas spring subsystem that supports a deadload whilst the electromagnetic system provides the dynamic forces.

17 Such a sealed machine may also function as a fluid pump or as a mechanism by which fluid energy may be efficiently converted to electrical energy, the wireless motor being driven in reverse.

18. The technology is fully scaleable and may be applied to electrical machines having a wide range of sizes and power outputs.

Claims

Claims 1. An electromagnetic machine comprised of two parts, one magnetic and the other electrical, the first part consisting in at least one array of paired magnetic poles, whose poiarity is spatially periodic along or parallel to the locus of motion of the machine, the paired arrays being aligned with opposite magnetic poles facing so as to produce a series of magnetic fields transverse the second part, of alternating polarity and having a regular spatial period, the second part consisting in at least one array of electrical conductors placed between the or each pair of magnetic arrays of the first part and intersecting the transverse magnetic flux, the conductors each having area dimensions matching those of the magnetic poles and being spatially periodic in correspondence therewith, currents being arranged to flow in the electrical conductors of the second part so that there is produced by the direct interaction of the electric currents and the transverse magnetic fluxes an orthogonal electromagnetic force whose magnitude and sign may be controlled by the said currents, the two parts of the machine being so constructed that one is constrained to move relative to the other along or parallel to the electromagnetic force vector, characterised in that the electrical conductors of the second part are formed as a regular pattern within at least one lamina of electrically conductive material having no substrate.
2. A machine constructed in accordance with claim i in which a plurality of electrically conducting laminae of the second part are overlaid and interdigitated to form a substantially planar mechanical structure.
3. A machine constructed in accordance with claims I or 2 in which at least one of the spatially periodic transverse magnetic fields of the first part is produced by the use of permanently-magnetised material.
4. A machine constructed in accordance with claims 1 or 2 in which at least one of the spatially periodic magnetic fields of the first part is produced by means of wire coils or of patterned laminar conductors through which electric currents are caused to flow when the machine is in operation
5. A machine constructed in accordance with claims I or 2 in which the spatially -periodic magnetic fields of the first part are induced by temporal variation of the currents in the conductors of the second part.
6. A machine constructed according to claims 1 or 2, in which at least one conducting lamina is made from insulated patterned metallic sheet, strip, ribbon or foil.
7. A machine constructed according to any preceding claim in which the laminar conductors of the second part are connected in a plurality of phases, through which separate electrical currents are arranged to pass, the relative signs and amplitudes of the said currents being controlled so as to determine the magnitude and sign of the electromagnetic force produced by the machine.
8. A three-phase machine constructed according to ciaim 7, in which the patterns of electrical conductors formed within the laminae of each phase include conducting paths transverse to the force vector and having a regular spatial dimension that is approximately equal to but less than one sixth of the length of the magnetic period and which cause the current to flow alternately back and forth transverse to the line of the force vector with a spatial period equal to one half of the magnetic period, the conducting paths of each phase being arranged to lie adjacent those of the other two phases in the region of the spatially-periodic magnetic field and to overlap them elsewhere.
9. A machine constructed in accordance with any of the preceding claims in which the magnetic fields are produced by the armature and the electrical conductors constitute or are incorporated within the stator.
10. A machine constructed in accordance with any of the preceding claims in which the magnetic fields are produced by the stator and the electrical conductors constitute or are incorporated within the armature.
11. A machine constructed in accordance with any of the preceding claims, in which the armature is arranged to move through or along at least one bearing affixed or forming part of the stator.
12. A machine constructed in accordance with claim 11 in which the armature force-carrying element emerges from or is carried by the stator bearing asscmbly.
13. A machine constructed in accordance with claim ii in which at least one end of the machine has an aperture and carries a cylindrical bearing through which is extended a thrust tube or rod by which the force on the armature may be transmitted externally.
14. A machine constructed in accordance with claim II, in which the armature is external to the stator, the armature being coupled to the load by any convenient method.
15. A machine constructed in accordance with claim 14 in which the electric currents of the stator interact with a plurality of armatures travelling along at least one bearing or track coincident with or parallel to the centre line of the stator.
16. A machine constructed in accordance with claim 15 in which at least one of the bearings or tracks forms part of the stator assembly.
17.A machine constructed in accordance with any preceding claim in which the electrical conductors of the stator are divided into sectors along the line of motion of the or each armature and may be independently powered and controlled so as to improve the efficiency of the machine or to provide independent control to a plurality of armatures sharing the same stator structural assembly.
18. A machine constructed in accordance with any of the preceding claims, in which there is no fin or rod extended so as to connect to an internal armature but in which the load is connected to the stator and thereby receives the whole or part of the reaction forces corresponding with the accelerations of the unconnected armature.
19. A machine constructed in accordance with any of the preceding claims, in which the centre line of the stator is not rectilinear but may describe an arc of a circle, the armature being of a predetermined shape so that it may move smoothly along the curved axis of the stator
20.A machine constructed in accordance with claim 19, in which the arc of the centre line of the machine stator is extended to form a complete circular channel and is closed upon itself to form a torus of rectangular cross section.
21. A machine constructed in accordance with claim 19, in which the armature is mechanically connected to at least one disc or wheel by which the rotational torque produced by the electromagnetic forces on the armature may be conveyed to a shaft whose axis is coincident with the central axis of the torus formed by the stator
22. A machine constructed in accordance with claim 19 in which the centre line of the stator channel is not planar but follows a smooth curve in three dimensions, such as a spiral.
23. A machine constructed in accordance with claim 19, in which the armature assembly is flexible or articulated and may follow any smooth locus of motion in three dimensions within the limits of practical design.
24. A machine constructed in accordance with any of the preceding claims, in which the laminar conductors of the second part are arranged to make good thermal contact with at least one cap beam having a low thermal resistance and being arranged to include or to be in good thermal contact with channels for cooling fluid or with a secondary component that constitutes a heat sink or heat dissipator.
25. A machine constructed in accordance with any of the preceding claims, in which at least one of the laminar conductors includes or supports a layer of material which, when cooled below its critical temperature, becomes superconducting.
26. A machine constructed in accordance with any of the preceding claims, in which at least one of the laminar conductors includes or is fabricated from ferromagnetic material.
27. An electromagnetic machine that consists in a concatenated plurality of individual (or elemental) motors, at least one of which is constructed in accordance with at least one of the preceding claims, some or all of the elemental motors being coupled mechanically so as to combine their output actions.
28. An electromagnetic machine constructed in accordance with claim 27, in which at least one elemental motor has a magnetic array in common with at icast one of its neighbouring elemental motors.
29. A machine constructed in accordance with claim 27, in which the elemental motor is a rotary motor in accordance with either of claims or 21
30. A machine constructed in accordance with claim 27 in which the elemental motor is a linear motor in accordance with any of claims I through 26 excepting claims 20 and 21.
31. An electromagnetic machine constructed in accordance with claim 30, in which the concatenated plurality of individual motors is not rectilinear but closes upon itself to form a polygon or an approximation to a circle of elemental machines.
32. A machine constructed in accordance with claim 31, having an even number of individual motor elements
33. A machine constructed in accordance with claims 30 or 31 and configured within a cylindrical container.
34. A machine constructed in accordance with claim 33, in which at least one end of the containing cylinder has an aperture and carries a bearing through which is extended a thrust tube or rod so as to convey the total force on the armature array to an external load.
35. A machine constructed in accordance with claim 34 in which a volume that includes the containing cylinder is hermetically sealed and the emerging thrust rod or tube is arranged to pass through a sliding seal, so that the armature may have both an electrical and a pneumatic function.
36. A machine constructed in accordance with claim 35, in which the thrust rod or tube forms the active element of a gas spring.
37. A machine constructed in accordance with any preceding claim excepting claims 14, 15 or 16, in which the armature is external to the stator, the external armature being coupled to the load by any convenient method.
38.A machine constructed in accordance with any of claims 27,28 or 30 through 37, in which the electrical conductors of the concatenated assembly are divided into electrically-isolated sectors along the axis of the machine.
39.A machine constructed in accordance with claim 38, in which a plurality of concatenated armatures move relative to a concatenated stator assembly.
40. A machine constructed in accordance with any of the preceding claims, in which impulsive electromagnetic forces on the armature are transmitted to the load via the equal and opposite reaction forces experienced by the stator.
41. A machine constructed in accordance with claim 35, in which the movement of the armature is arranged to propel or to be propelled by fluid within the enclosed stator, so as to function as a pump or to absorb energy from a moving fluid.