GB2171854A - Direct current machine - Google Patents

Description

1 GB2171854A 1

SPECIFICATION

Direct-current machine and method of manufacturing same The present invention relates to a direct-current machine, and a method of manufacturing the same, particularly a collector-type D.C. machine, whether a motor or a generator, having a multi-pole stator magnet arrangement and an ironless rotor winding comprising a plurality of rotor coils lower in number than the number of stator poles, with the rotor coils being arranged as a single- layer winding and with the collector of the machine comprising collector lamellas of which predetermined ones are electrically interconnected by crossconnecting means. Such a machine is disclosed, for example, in Federal Republic of Germany Patent Application P 32 17 283.4.

It is the general object of the invention to improve and simplify motors of such known type, as well as their manufacture.

In accordance with one aspect of the inven tion, there is provided a direct-current machine comprising:

(a) a stator including an eight-pole stator magnet arrangement; (b) a six-coil ironless rotor arrangement which is mounted for rotation about a rotor axis and which includes six coils arranged in a single winding layer at equiangular intervals about the rotor axis and a collector arrange ment having twelve collector lamellas arranged in a circle about the rotor axis, the angular 100 spacing between corresponding points of suc cessive lamellas accordingly being substantially mechanical degrees, the twelve collector lamellas consisting of first, second and third collector lamella groups, and each collector la- 105 mella group consisting of a respective four collector lamellas spaced one from the next at angular intervals of 90 mechanical degrees; and (c) means for transmitting current to and from the collector lamellas and for electrically connecting together respective collector lamel las, said means including first and second brush arrangements on the stator electrically engaging collector lamellas and angularly off- 115 set from each other by about 45 + n X 90 mechanical degrees, wherein n = 0 ' 1,2 or 3 and said means further including cross-connecting means operative for causing the four collector lamellas of respective collector]amella groups to be electrically connected together as successive collector lamella groups are electrically engaged by the first and second brush arrangements, wherein the six coils consist of first, second and third coil-pairs, with each coil-pair being constituted by two coils located diametrically opposite each other with respect to the rotor axis, the two coils of each coil-pair are connected 130 in series with each other, and the first, second end third series-connected coilpairs are, respectively, electrically connected between collector lamellas of the first and second collector lamella groups, between collector lamellas of the second and third col lector lamella groups, and between collector lamellas of the third and first collector lamella groups.

Preferably, the cross-connecting means corn prises first, second and third cross-connecting means provided on the rotor arrangement, each cross-connecting means permanently electrically connecting together the four collec- tor lamellas of a respective one of the first, second end third collector lamella groups.

With such a construction one obtains, with a good copper packing factor, a simple manner of production, since only a few connecting operations are required to establish the few electrical connections to the collector. This is particularly of advantage in the case of miniature motors, such as the present invention preferably concerns. Such motors typically have powers lower than 10 watts. Also, such motor construction exhibits a symmetrical rotor configuration and, all in all, an extremely compact structure.

According to a preferred embodiment of the invention, the constituent rotor coils of the rotor winding are formed by a single, uninterrupted conductor which is wound without break from one coil to the next, thereby maintaining low the number of wires which need be connected to the collector.

In many cases a low axial moment of inertia of the rotor is desired, for example, in order to assure quick motor start-up. According to a further embodiment of the invention, the rotor coils are mounted on the rotor at their radially innermost parts and extend out from there in cantilevered and self-supporting fashion. In this way, the axial moment of inertia of the rotor is determined substantially exclusively by the inherent weight of the rotor coils themselves. At the same time, the rotor coils are surrounded by air on all sides and thus experience a particularly good cooling action, so that they may be safely subjected to rather high thermal loading.

The invention furthermore contemplates particularly convenient ways of fabricating the collector. Accordingly, a second aspect of the invention provides a method of manufacturing a planar-geometry collector having a circular succession of collector lamellas and at least one cross-connecting means which electrically connects together predetermined ones of the collector lamellas to form a collector lamella group, the method comprising initially forming such a collector in which the cross-connecting means electrically connects together collector lamellas in addition to said predetermined ones of the collector lamellas, and then destroying the electrical connection between the 2 GB2171854A 2 crossconnecting means and collector lamellas other than said predetermined ones of the collector lamellas.

In addition to the objects and advantages stated above, further objects and advantages will become apparent from the description of specific embodiments when read in connection with the accompanying Figures in which:

Fig 1 schematically depicts a first embodi- ment of the inventive machine, here with a flat air gap, an eight-pole stator magnet, a rotor comprised of six equiangularly arranged rotor coils, and a collector having twelve collector lamellas; Fig 2 schematically depicts the collector of Fig 1 including three cross-connecting means and anti-interference capacitors; Fig 3 depicts the rotor winding of Fig 1, strung out to show the manner in which the six rotor coils can be fabricated using only a 85 single conductor which proceeds without break from one coil to the next; Fig 4 is a longitudinal section through a pre ferred embodiment of a motor having the ro tor-coil and statormagnet arrangement of Fig 1, depicted at a greater than true scale; Fig 5 is a plan view of the collector of the motor of Fig 1, seen from the brush side, at enlarged scale, with certain parts of the struc ture broken away to facilitate visualisation; Fig 6 is a section, taken along line VINI of Fig 7, through a spring element which servss to press an anti-interference circuit module into position against the collector, and which furthermore serves as a crossconnecting means interconnecting four collector lamellas; Fig 7 is a plan view of the spring element of Pig 6, seen along line VII of Pig 6; Fig 8 depicts a collector blank at an early stage of fabrication of the collector, seen from the brush side, with an orientation corre sponding to that of Fig 5; Fig 9 is a section through the collector blank of Fig 8, taken along line IX-IX of Fig 8, the orientation of the blank being upside-down 110 in Fig 9 compared to Fig 8; Fig 10 is a view of the collector blank as shown in Fig 9, in finished state, embedded in a molded body of insulating material, an anti interference circuit module being shown in po sition in dash-dot lines; Fig 11 is a longitudinal section like that of Fig 4 but of a second embodiment of an in ventive collector-type D.C. machine of sym metrical construction, a portion of the struc- 120 ture at the left side being removed to facilitate visualization, the depiction being at about four times typical true scale; Fig 12 is a partially sectioned side view of the carrier member of the motor construction of Fig 11; Fig 13 depicts a molded rotation-transmitt ing member of the machine of Fig 11; Fig 14 is an end view of the carrier member of Fig 12, additionally showing, in dash-dot lines, the position of a rotor coil, and furthermore showing the location of connecting wires; Fig 15 depicts the carrier member of Figs 12 and 14 with the rotor coils and collector mounted in place; Fig 16 is a vlew of the structure of Fig 15 seen from below; Fig 17 is a longitudinal section, like that of Figs 4 or 11, through a third embodiment of an inventive collector-type D. C. machine, on a larger than true scale; Fig 18 illustrates in plan view the arrangement of stator magnets and brushes on the yoke plate of the machine of Fig 17; Fig 19 is a section through an element of the rotor of the machine of Figs 17 and 18, such element serving as a carrier member for the rotor coils and for the flat collector; Fig 20 is a plan view of that face of the element of Fig 19 on which the rotor coils are to be mounted; Fig 21 is a plan view of the flat collector of the motor of Figs 17-21, in incompletely fabricated condition; Fig 22 is a plan view of the flat collector of Fig 21, in finished condition; and Fig 23 is a plan view of the carrier member of Fig 19 and, mounted thereon, six equiangu- larly spaced rotor coils, as well as the connections of the rotor coils to the collector and to an anti-interference circuit module.

In the various Figures, identical or corresponding elements are denoted by identical reference numerals. Terms such as "upper", "lower", "left", "right" refer to the orientation of a particular structure as depicted in a particular Figure. To impart a notion of typical true scale, a -1 cmlength designation ap- pears in various Figures, but the exact dimensions of particular depicted structures can of course be larger or smaller.

Fig 1 is a schematic plan view of a first embodiment of a machine 20, in this instance a machine having a flat air gap, and in particular is a view taken along a section plane parallel to the air gap. Depicted are a collector 22 having twelve collector lamellas 1-12, six rotor coils A-F and, behind the latter, a stator mag- net 21 which has eight poles and is axially magnetized. Typically, the stator magnet may be a one-piece annular member polarized in the illustrated manner and has a plot of induction versus angular location, along the circumferential direction of the stator magnet, with the shape of a trapezoid wave. However the stator magnet could alternatively comprise, for example, an assembly of discrete magnet segments. The radial extent of the stator magnet ring is such as to cover the magnetically active sections of the rotor coils A-F that is, the portions of the latter extending generally in a radial direction. Fig 1 depicts the stator magnet ring extending radially outwardly to an exaggerated degree, beyond the radially outer 3 GB2171854A 3 periphery of the set of six rotor coils, merely to facilitate visualisation of the angular extents of the successive stator poles.

Fig 2 depicts, in a likewise very schematic manner the electrical interconnections amongst constituent elements of the collector 22, in this instance depicted as a generally planar collector. It will be appreciated, however, that other collector geometries could be employed.

Of the twelve collector lamellas 1-12, lamellas 4,8 and 12 are each provided with a respective bent-up conductive tab for a 8A, 12A. As will be explained below, the bent-up conductive tabs 4A, 8A, 12A serve as electrical contacts which form conductive connections to an antiinterference circuit module. The latter comprises three identically dimensioned capacitors or condensors 23, 24, 25 as shown in Fig 2. Capacitor 23 is connected between conductive tabs 4A and 8A capacitor 85 24 between tabs 8A and 12A and capacitor 25 between tabs 12A and 4A.

As shown in Fig 2, the twelve collector lamellas 1-12 are electrically interconnected by three cross-connecting means, as follows:

A first cross-connecting means 26 electri cally connects together the four collector la mellas 2,5,8,11 of a first collector lamella group; A second cross-connecting means 27 elec- 95 trically connects together the four collector la mellas 1,4,7, 10 of a second collector lamella group; and A third cross-connecting means 28 electri cally connects together the four collector la mellas 3,6,9,12 of a third collector lamella group.

In the instance depicted in Fig 2, the set of twelve collector lamellas is thus subdivided into three collector lamella groups, each constituted by a respective four collector lamellas, the four lamellas of one group being spaced from one another at intervals of 90 mechanical degrees.

Two brushes 30,31 are employed to 110 transmit current to and from collector lamellas 1-12. The brushes 30,31 are not located diametrically opposite each other. Instead, one brush, namely, brush 30, is mounted on the stator beneath a north pole segment of the stator magnet 21, and the other brush, here brush 31, beneath a south pole segment, the angular spacing between the two brushes being 45 + n X 90 mechanical degrees, wherein n= 0, 1, 2 or 3.

It is to be noted that, as an alternative to the rotor-mounted crossconnecting means 26, 27, 28 equivalent cross-connections could be established by using, instead of one brush 30 and one brush 3 1, two sets of brushes, each set of brushes being constituted by four brushes, with the four brushes of one set being angularly offset by about 45 mechanical degrees from the four brushes of the other set. In such a case, the four brushes of one set of brushes would be electrically connected to one another, and the four brushes of the other set would be electrically connected to one another.

In this first embodiment, the set of six rotor coils A-F is provided with a total of only three external connection points 32,33,34 and these are, as shown, electrically connected to respective ones of the three collector lamellas 1,5,9. In this respect, reference is made to Fig 3, which illustrates the manner in which the six coils A-F are fabricated as a continuous- conductor chain of coils. As can be seen from a comparison of Figs 1 and 3, the six rotor coils A-F are organized as three coilpairs A,B; C,D; and E,F. The two coils of each coil-pair A,13 or C,D or E,f are located diametrically opposite each other, relative to the rotor rotation axis.

As shown in the embodiment of Fig 3, the six rotor coils A-F may be wound from a sin gle conductor which extends without break from one coil to the next. The single conductor, in addition to the portions thereof forming the six coils per se, comprise transitional portions which extend from one coil to the next. These transitional portions are either inter-coil transitional portions, which extend a distance L, from one coil of a coilpair to the other coil of the same coil-pair, or else are inter-coil-pair transitional portions which extend a distance L, from a coil of one coilpair to a coil of a neighbouring coil-pair. As shown, the inter-coil spans L, are greater than the inter-coil pair spans L, The ratio L,:L, can preferably be of the order of 3:2 or 4:3.

As shown in Fig 3, the inter-coil-pair transitional portions of the constituent conductor each extend first from a coil of one coil-pair to a respective connection point, at 33 or 34 or 32, and then from such a connecting point to a coil of an adjoining coil-pair. The connection point 32A, 32F is electrically connected to the collector lemella 1. The connecting point 33 is electrically connected to the collector lamella 5. The connection point 34 is electrically connected to the collector lamella 9. As will be appreciated from Fig 1, each of the six coils A-F is symmetrical with regard to a re- spective symmetry plane which passes through the rotor rotation axis, and the three connection points 32,33, 34 are spatially located near adjoining coils but angularly offset by a distance d, as shown In Fig 3, relative to the symmetry plane of the respective coil. As also indicated in Fig 3, all six coils A-F have the same winding sense.

During assembly of the machine, the rotor coil A may be secured at a location where its symmetry plane coincides with the radial line of separation between collector lamellas 10 and 11, as shown in Fig 1, with coil B then being located diametrically opposite thereto. Then, coil C of Fig 1 is secured adjoining coil B, with the symmetry plane of coil C coincid- A 4 GB2171854A 4 ing with the line of separation between collector lamellas 2 and 3, with coil D being then positioned diametrically opposite coil C. Then, coil E is secured in place alongside coil D, with the symmetry plane of coil E coinciding with the line of separation between collector lamellas 6 and 7, as shown in Fig 1, and coil F is then secured in place diametrically opposite Coil E. Electrical connection of the con- necting points 32,33, 34 to respective collector lamellas has already been described above.

Naturally, the connection point 32A, instead of being connected to collector lamella 1, could equivalently be connected to any of la- mellas 4,7 or 10, since the four collector lamellas 1,4,7,10 are anyway electrically connected together by the second cross-connecting means 27. Thus. and expressed in another way, in the illustrated embodiment the coil connecting point 32 is electrically connected to the second crossconnecting means 27; the coil connection point 33 to the first crossconnecting means 26; and the connection point 34 to the third crossconnectting means 28. Expressed yet another way, the three series circuits A-B, C-D, E-F are connected in delta configuration between the three crossconnecting means 26,27, 28.

As will be apparent from the above descrip- tion, the fabrication of the six rotor coils A-F, by virtue of their formation from a single, uninterrupted, continuously wound conductor, is very simple, and likewise simple is their assembly and their electrical connection to col- lector 22. These are extremely simple and suitable for automated performance, especially as only three soldering or welding operations are required. Due to the offset d of the individual connection points 32,33, 34, there results automatically the correct positioning of the coil ends relative to the associated collector lamellas.

The individual rotor coils are preferably fabricated with a cementing or binding lacquer or varnish causing the coils to be inherently shaperetaining, so that they may be mounted, as described below, in a selfsupporting or cantilevered fashion. Where the aforementioned transitional portions of the constituent conductor cross the coils, such lacquer or var- 115 nish is absent. For example, the transitional portion 36 (Fig 3) extending from coil B to coil C is not provided with such lacquer or varnish along segment 37 thereof. The same is true in similar fashion for the other coils. In the assembled condition of the machine, the transitional portions of the rotor coils' con stituent conductor are located beneath the col lector, where they can be securely cemented.

Fig 4 depicts, on a greatly enlarged scale, a preferred embodiment of the mechanical con struction of such a machine, in this instance a drive motor for the capstan of a signal-record ing device for video signals. This device corn prises a carrier pipe 40 with a mounting 130 flange 41. A motor shaft 43 is journalled in roller bearings in the carrier pipe 40, only one roller bearing unit 42 being illustrated. A carrier member 44, made of non-magnetic ma- terial, such as aluminum, is secured at a hub portion 45 thereof to the motor shaft 43. Secured to the underside 46 of the carrier member 44, for instance, by means of cement, are the radially inward portions of the rotor coils A-F, of which two are illustrated in Fig 4 and are donated at 47 and 48, the remaining portions of the rotor coils extending radially outwardly therefrom in cantilevered fashion. The carrier member 44 can, for example, have. an external diameter of 4.4 cm, whereas the overall circular outer periphery of the set of six rotor coils may have a diameter of about 7.8 cm. In this way, the axial moment of inertia is determined for the most part only by the six rotor coils themselves. Accordingly, the axial moment of inertia, the so-called GD2, of such a rotor 50 is very small and, at the same time, the individual coils 47,48 experience a very effective cooling action and thus can be safely subjected to high thermal loading.

The rotor coils 47,48 freely extend radially outwardly,with their magnetically active segments projecting into a flat air gap 53 formed between a stator magnet ring 54 and an annular flux-return or voke plate 55 made of iron. As shown in Fig 1, the stator magnet ring 54 has eight poles and is axially magnetized. The yoke plate 55 is held in place, by magnetic attractive force, against the edge of the outer peripheral wall 56 of an annular channel-like stator housing 57. The stator housing 57 is a deep-drawn sheet-steel part and accommodates in its interior the magnet ring 54 which is cemented in place. Stator housing 57 is secured to the mounting flange 41 at locations 58,59 by any appropriate conventional means and, as shown in Fig 4, has an inner peripheral wall 61 which is centered on the carrier pipe 40.

Secured to the bottom face of the yoke plate 55 is a moulded part 62 made of electrically insulating material and mounting the two brushes 30,31 of which only brush 30 is, in part, visible in the sectional view of Fig 4. The brush 30 is secured at the base portion thereof to a damping mass 63 which serves to attenuate mechanical oscillations of the elongate body of the brush. The collector 22 is secured on the hub portion 45 of the carrier member 44. The collector 22 comprises a hub member 65 made of an electrically insulating material in which are embedded the radially inner portions of the collector lamellas 1-12. The construction and manner of production of the collector 22 and its embedding hub member 65 will be explained below in greater detail in conjunction with Figs 5-10.

In fabricating the collector 22, one commences with a sheet-metal blank 66 which GB2171854A 5 has been stamped out to provide the configuration depicted in Fig 8. As shown in Fig 8, at this stage of fabrication the twelve collector lamellas 1-12 are still all electrically interconnected with one another. The first cross-connecting means 26, however, is already present in the stamped blank of Fig 8 and, as shown, electrically connects together the collector lamellas 2,5,8,11 at the radially inner portions thereof. The first cross-connecting means 26 is already electrically separated from the other eight collector lamellas by virtue of arcuate cut-outs 67. The bent-up conductive tabs 4A,8A,12A, schematically depicted in Fig 2, are already present on the stamped-out blank of Fig 8 in bent-up condition, as better seen in Fig 9, described below. The tabs 4A,8M2A are located radially outwardly of the circular zone swept over by the brushes 30,31.

Fig 9 is a section through the stamped-out blank 66 of Fig 8, taken along line IX-1X. It is to be noted that in Fig 9 the blank 66 is shown upsidedown with respect to its depic- tion in Fig 8. Thus, in Fig 8, tab 4A appears above tab 12A, whereas in Fig 9 tab 12A appears above tab 4A. The orientation of the blank, as depicted in Fig 8, corresponds, however, with the orientation of the blank as viewed in Fig 5, yet to be described.

In the stamped-out blank 66 of Fig 8, the second cross-connecting means 27 is present only in rudimentary form, to the extent of four arcuate cutouts 68 located radially outwardly of the operative range of the brushes. In the circular zone in which the brushes will sweep across the collector lamellas 1-12, the collector lamellas are, in the stamped-out blank of Fig 8, already separated one from the next by radial gaps 69. The radial lamella-separating gaps 69 extend radially outward past a circle 72 and, in the region of circle 72, have enlarged portions. The bent-up conductive tabs 4A, 8A, 12A are likewise located on the cir- cle 72.

After fabrication of the collector blank 66 of Figs 8 and 9, the blank is embedded is a moulded body of synthetic plastics material, preferably a polyamide, the moulded body having the form shown in Fig 10 and, in plan view, in Fig 5. As shown in Fig 10, such a moulded body has a central hub portion 65 which completely envelops the first cross-connecting means 26, completely fills the afore- mentioned arcuate cut-outs 67, and entirely envelops and embeds the radially inner portions of the collector lamellas 1-12. In the vicinity of circle 72, Figs 8, 10 and 5, the moulded insulating member comprises a ring portion 75 which is located to both axial sides of the collector blank 67 and, in this vicinity, envelops the collector lamellas from both sides. The material of ring portion 75 passes through the enlarged portions of the radial gaps 69 (Fig 8) at the region of the circle 72, and, likewise, passes through the circular apertures located intermediate adjoining enlarged portions of the gaps 69. Spoke-like portions 76 extend integrally from the radially inner hub portion 65 to the ring portion 75.

After the stamped-out collector blank 66 has been thus embedded in insulating material, it is then subjected to a further stamping procedure, serving to complete the fabrication of the second cross-connecting means 27, such that the latter is electrically continuous only with the collector lamellas 1,4,7,10. One example of the way in which this may be accomplished can be seen in Fig 8 wherein further cut-outs, 77,78,79 may be stamped out to extend the three associated radial gaps 69 out to the associated arcuate cut-out 68. This serves to electrically separate the two collector lamellas 11,12 from the second cross-connecting means 27. Three further sets of such cut-outs 77,78,79 are likewise formed, to electrically separate the second cross-connecting means 27 from the two collector lamellas 2,3 from the two collector]a- mellas 5,6, and from the two collector lamellas 8,9. When this further stamping-out procedure has been completed, the radially outward zone of the collector blank will now have the appearance shown in Fig 5.

The first group of four collector lamellas 2,5,8,11 are continuous only with the radially inward first cross-connecting means 26, and this first continuous area from the original blank is shown in Fig 5 hatched in by tiny dots.

The second group of four collector lamellas 1,4,7,10 are continuous only with the radially outward second cross-connecting means 27, and this second continuous area, formed from the original blank, is shown in Fig 5 hatched in by short fleck-like straight lines.

The third group of four collector lamellas 3,6,9,12 not hatched in Fig 5, are, at this stage of fabrication, discontinuous from one another and discontinuous from all the remainder of the original blank. The third cross-connecting means 28, which electrically connects these four lamellas together, is yet to be provided in a manner described below.

Before that, it is to be noted from Fig 10 that the three bent-up conductive tabs 4A,8A,12A, already described project axially out of the insulating ring portion 75 and are spaced angularly by 120' as shown in Fig 8.

The three tabs 4A, 8A, 12A are employed as electrical contacts and electrically engage three electrical contacts of an annular antiinterference circuit module 82. The annular module 82 may, for example, be a cast or moulded synthetic plastics body whose interior accommodates the three anti- interference capacitors 23,24,25 of Fig 2. The insulating ring portion 75 is provided with three integral centering pins 83 which serve to centre the annular cir- cuit module 82. The three centering pins 83 6 GB2171854A 6 are received in recesses in the axial end face of the annular housing of module 82, to posi tively define the position of the circuit module.

However, the right end face, as viewed in Fig 10, of the circuit module 82 axially bears only against the three bent-up contact tabs 4A,8A,12A, in order to establish a purely three-point support against the contact tabs.

This assures that electrical engagement will be reliably established anmaintained with the three contact tabs.

The annular circuit module 82 is axially pressed against the tabs 4A 8A,12A by means of a spring member 84 shown mounted in place in Fig 4, and shown sepa- 80 rately in Figs 6 and 7. The spring member 84 has a central annular portion 85 which en circles the hub member 65, as shown in Fig 4. The central portion 85 bears axially against the antiinterference circuit module 82, pressing the latter against the conductive tabs. Extend ing radially outwardly from central portion 85 are four identical spoke-like spring arms 86,87,88,89 of somewhat Z-shaped configu ration. The free ends of these four spring arms are planar and extend approximately par allel to the plane of the central annular portion 85.

This spring member 84 is simultaneously employed as the third cross-connecting means 28. As shown in Fig 5, the planar ends of the four spring arms 86,87,88,89 are each perma nently welded to a respective one of the four collector lamellas 3,6,9,12 of the third collec tor lamella group, electrically interconnecting 100 them. The welding location is radially out wardly of the insulating ring portion 75.

As shown in Fig 5, the connection points 32,33,34 for the rotor coil-pairs are respec tively connected, by soldering, to the collector 105 lamellas 1,5,8, radially outwardly of the insu lating ring portion 75.

From the foregoing description,it will be ap preciated that the collector arrangement de picted in Fig 5 constitutes an extraordinarily compact structure whose fabrication can be performed with a remarkably low number of operations. The span of the coils is, as illus trated, preferably greater than 180 electrical degrees. Sector-shaped coils such as here il lustrated are preferred, but circular coils could likewise be employed.

If it should be desired to replace the three cross-connecting means 26,27,28 by brushes, then in addition to brush 31, three further such brushes must be provided, respectively offset relative thereto by 90', by 1800 and by 270' and all electrically connected to brush 31. Likewise, in addition to brush 30, three further brushes would be required, likewise offset relative thereto by 90', 180' and 270' and all electrically connected to brush 30.

Self-evidently, the collector 22 can have an angular position relative to the coils A-F other than the one illustrated, provided that the 130 brushes 30,31 are likewise shifted by such angle. The spacing d of Fig 3 will then have a different magnitude and could also be of zero magnitude.

The illustrated motor has a power consumption of 0.6 W and at 1500 rpm produces a torque of 0.2 Ncm (20 cmp), and is a miniature motor which supplies a torque of very good constancy with a very low axial moment of inertia.

Fig 11 depicts, at a scale considerably greater than typical true scale, a second embodiment of the invention. Here a drive motor is used for a signal-recording device for video signals. This device comprises a carrier pipe 140 with a radial mounting flange 141. A motor shaft 143 is journalled in roller bearings accommodated within the carrier pipe 140, only one roller bearing unit 142 being illus- trated. A carrier member 144 of non-magnetic material, e.g. aluminium or a suitable synthetic plastics material, is secured to the motor shaft 143 at an axial extension 145 of the carrier member 144. The rotor coils 147, 148, of Fig 16, are secured at their radially inward portions to a peripheral stepped face of the carrier member 144 by means of cement. For instance, as illustrated by means of a thin fabric layer 151 impregnated with epoxy resin.

The carrier member 144 can have an outer diameter of, say, 2.8 cm, whereas the circular arrangement of six rotor coils has a general outer periphery having a diameter of 5.7 cm. For example, the axial moment of inertia is determined substantially exclusively by the six rotor coils per se, so that the rotor 150 has a very small GD2 value, while at the same time the individual rotor coils 147,148 experience very good cooling action and can be safely subjected to high thermal loading.

The coils 147,148 extend with their magnetically active sections into a flat air gap 153 formed between an upper stator magnet ring 154 and a lower stator magnet ring 155. The two stator magnet rings 154,155 are axially magnetized at each of eight poles. An annular flux-return or yoke plate 152 made of iron carries the magnet ring 155 and is held, by magnetic holding force, against the rim of the outer peripheral wall 156 of a cup-like stator housing 157. Stator housing 157 is a deepdrawn sheet-steel part, and the upper magnet ring 154 accommodated therein is cemented in place. The stator housing 157 is secured, by means of screws 158, to a flange 141 and, as illustrated, is at its radially inner rim 161 centered on the carrier pipe 140.

Secured to the bottom face of the yoke plate 152, by means of screws 183, is a moulded member 182 made of an electrically insulating material and mounting two brushes, of which only the brush 130 is visible in Fig 11. The screws 183 extend through apertures 184 in the moulded insulating member 182. The apertures 184 are, if viewed axially of the 7 GB2171854A 7 motor, of elongate or arcuate extent, thereby permitting angular shifting of the member 162 relative to the rotor axis of the motor, say, before tightening of screws 183. This makes it possible during assembly to establish an optimum position for the brushes 130 relative to the stator magnet rings 154,155.

A collector 122 of planar geometry is mounted on the axial extension 145 of the carrier member 144. The collector 122 includes a hub member 165, made of an electrically insulating material, which securely embeds the radially inward ends of the collector's twelve collector lamellas. The collector 122 may be of the same construction, and fabricated in the same way, as already described with respect to Figs 5-10. Likewise, the eight-pole magnetization of the magnet rings 154,155 may be the same as already described with reference to Fig 1. Also, the arrangement of the rotor coils and their electrical connections to one another and to the collector lamellas may be the same as already described with regard to Figs 1-3. As shown in Fig 16, the rotor coils may here be circular, and fabricated with cementing or binding varnish or lacquer, to impart to the coils shaperetaining properties permitting them to be mounted in cantilevered or self-supporting manner. Of course, use could alternatively be made of one or more discrete coil carrier member, although the illustrated cantilevered mounting of the rotor coils is preferred.

Located above the collector 122 is an annu- lar anti interference circuit module 182 containing three capacitors, whose manner of connection is shown in Fig 2 as is also the arrangement of its collector brushes.

As furthermore shown in Fig 11, the carrier member 144 has a maximum outer diameter which is smaller by only about 2 mm than the inner diameter of the magnet ring 155 which encircles it, so that the gap 160 between the lower magnet ring 155 and the outer peri- phery of the carrier member 144 amounts to only about 1-1.5mm. So small a gap is important, in order that there be provided in the vicinity of the magnetically active sections of coils 147, 148 a magnetic field of the great- est possible homegeneity.

If now the connecting lines for the coils 147,148 were to be led through this narrow gap 160, then during assembly or later repairs the connecting lines could easily become wedged in the gap, and thereby be badly damaged or destroyed. For this reason, as shown in Figs 12 and 14, the carrier member 144 is of non- circular configuration at its outer periphery. In particular, the carrier member 144 is of greatest radius at those locations thereof where a coil 147 is to be secured thereto. Between such locations it is of somewhat reduced radius, so that at such locations the connecting lines 185 for the collector 122 can be fed through and fixed in place by means of cement, or the like, at a location such as indicated in Fig 14 at 166.

At its inner periphery 167, the carrier member 144 encircles the carrier pipe 140, form- ing therewith a long and very narrow gap 168, so that grease or oil from the bearings 142 cannot migrate through this narrow gap to the collector 122, and thus not interfere with proper operation of the collector. To this end, the carrier member 144 is provided at its upper face with a relatively long collarlike extension 169.

The lower axial extension 145 of carrier member 144 is, as shown in Figs 11 and 12, provided with two flattened portions 171,172 which extend to the inner opening 173 provided for the shaft 143. Shaft 143 is likewise provided with two corresponding flattened portions, of which, in Fig 11 only, the flat- tened portion 174 is visible. A moulded part 175, as shown in Fig 13, has an internal opening 176 which is complementary to these flattened portions. As shown in Fig 11, the moulded part 175 is fitted on to the axial extension 145 and connects the latter with the shaft 143 for joint rotation therewith. Two dish springs 177 are provided, one bearing against a nut 178 screwed on to the lower end of shaft 143, the other bearing on the axial extension 145. The dish springs thus press the carrier member 144 upwardly against a shoulder 179 on the shaft 143, establishing a definite axial position for the carrier member 144. This same construction is employed in the case of the third embodiment, yet to be described.

Figs 15 and 16 depict the carrier member 144 when the collector 122 and the six rotor coils are in assembled and mounted condition.

The scale of the illustration is here likewise slightly larger than typical true scale. One can appreciate the very compact construction of the r tor 150 and its small axial moment of inertia, which makes possible very quick start- up of the motor in response to energization.

At an operating voltage of 10 V, the illustrated motor has a current consumption of 55 mA at 1500 rpm and rated load,that is, the load presented by the driven capstan. The type of motor here involved is a miniature motor exhibiting good efficiency, achieved with very compact construction. Tests have shown that such motors can be expected to have a very long service life.

Figs 17-23 depict a third embodiment of a D.C. machine according to the invention, here in the form of a miniature motor 200 which, as shown, has an axial thickness of about 8 mm and a diameter of about 40mm, and is thus extremely compact. This motor has a current consumption of about 180 mA at a D.C. voltage of 10 V at rated power, and at 1500 r p m produces a torque of about 0.2 Ncm with a starting torque of 0.95 Ncm. Be- cause of its extremely small dimensions, the 8 GB2171854A 8 motor 200 is illustrated on a considerably en- larged scale, especially in Figs 19-23. To facilitate appreciation of the correspondence between the scale of those Figures and that of Fig 17 and 18, a -1 cm- scale indication is provided for all those Figures. Motor 200 serves, for example, as the drive motor for a video-signal signal- recording device. A carrier structure 239 has a longitudinal bore 240 in which are mounted two roller bearings 241,242 for a motor shaft 243. Mounted on the shaft 243, by means of a synthetic plastics hub member 245, as shown in Fig 19, is a carrier member 244 which simultaneously serves for the motor's collector. The carrier member 244 is made of a glass-fibre-reinforced synthetic plastics material, such as, an epoxy resin, hard-as-glass web, having a thickness of 1.5 mm and laminated on both axial end faces with a thin copper layer of. say, 17.5 microns, the collector lamellas and the various requisite conductor paths being formed by etching away the portions of the copper layer not required therefor, in a manner described below. On the upper face 246 of the carrier member 244, the individual rotor coils 247,248 are directly secured thereto, at their radially inward portions, by means of cement, for example by means of an epoxy re- sin. In this third embodiment, the rotor coils have, as shown, a diameter of about 13 mm and a thickness of about 2.5 mm. The axial moment of inertia of the rotor is determined substantially exclusively by the rotor coils themselves.

The rotor coils 247,248 are provided with a cementing or binding varnish or lacquer imparting shape-retaining properties and they project radially outwardly in cantilevered fashion into a flat air gap 253 which is formed by the upper face of a set of eight round permanent magnets 254 of tabletlike shape having, say, a diameter of about 6 mm. As shown in Fig 18, these magnets 254 are mounted on an annular yoke plate 255 at equal distances from the rotor axis and at eguiangular intervals. The permanent magnets 254 are axially magnetized and have at the sides thereof, facing the air gap 253, alternately north and south poles, as shown in Fig 18, forming an eight-pole stator magnet arrangement. The magnets 254 are advantageously samariumcobalt magnets of high energy density. This makes it possible to dispense with the upper magnet ring 154 employed in the second embodiment, thereby decreasing the axial length of the motor.

Arranged on the yoke plate 255 are two brushes. Their insulated brush holders 256 are, in space-saving manner, each arranged in a respective interspace between two adjoining permanent magnets 254, the two brush holders 256 being angularly spaced by 135' from each other. The brush holders 256 have a shape mating with the outer peripheries of the 130 permanent magnets 254 as shown in Fig 18. The brush springs per se are angled members. Projecting from each brush holder 256 is a radial spring portion 257 from which, at an angle of about 158' thereto, there extends a further portion forming the actual brush 258. The brushes 258 are, as illustrated, longitudinally divided and extend tangential to the aperture 260 on the yoke plate 255. The ac- tual contact locations of the brushes 258, indicated in Fig 18 by radially extending dashdot lines at the brush ends, are, in the case of one brush, lined up with a south-pole magnet 254, and in the case of the other brush lined up with a north-pole magnet 254, with these two contact locations being spaced by an angular interval of 135'. Reference is made to the discussion of angle in a in connection with Fig 2. The yoke plate 255 is provided at its outer rim 255 with centering projections 259, of which one can be seen in sectional view in Fig 17. The yoke plate 255 has a central aperture 260 through which the free end of shaft 243 projects. This end of the shaft 243 is provided with an external thread, on to which is screwed a nut 263 which, through the intermediary of two dish springs 264, presses the hub member 245 upwardly. Hub member 245 has a flattened portion 265 as shown in Fig 19. which engages with a corresponding flattened portion 266 of shaft 243, as shown in Fig 17, to prevent the hub member 245 from turning relative to the latter.

A pan-like stator housing 271 is secured by means of screws 270 to the carrier structure 239 and is made of a magnetically conductive material, serving as part of the motor's magnetic-flux circuit. The flat base of the stator housing 271 has a central aperture which is centered on an axial projection 272 of the carrier structure 239. The bottom rim of the peripheral wall of the stator housing 271 mounts the yoke plate 255 which is held against such rim by the force of magnetic attraction, the marginal projections 259 of yoke plate 255 serving to centre the latter with respect to the rim of stator housing 271.

The air gap 253 is accordingly formed be- tween the permanent magnets 254 on the one hand and, on the other hand, the flat base of the pan-like stator housing 271. The brushes 258 are each provided with a lead 273 which exits the motor downwardly from out of the yoke plate 255.

Figs 21 and 22 illustrate the fabrication of the collector on the lower axial face 230 of the carrier member 244. As shown in Fig 21, twelve collector lamellas 201-212 are formed by etching away those portions of a copper coating not needed therefor, the copper coating being provided on a plate 244' which is later cut to form the carrier member 244. In similar fashion, there is formed a radially outer cross-connecting means 228 which electrically 9 GB2171854A 9 connects together the four collector lamellas 203,206, 209,212, in correspondence to cross-connecting means 28 of Fig 2. Likewise, by removing the portions of the copper coat ing not needed therefor, there is formed a radially inner cross-connecting means 226 which electrically connects together the four collector lamellas 202, 205, 208, 211 in cor respondence to cross-connecting means 26 of Fig 2. Lastly, on the reverse face of the plate 75 244', corresponding to the bottom face 230 of carrier member 244, there is formed, as shown in Fig 20, yet another such crosscon necting means 227 which electrically connects together the collector lamellas 201, 204, 207, 80 210 corresponding to the cross-connecting means 27 of Fig 2. Also, and as shown in Fig 21, for purposes of fabrication, there is ad ditionally formed a conductive path 229 con necting together the collector lamellas 210, 211 and 212 and located radially outwardly of the cross-connecting means 228.

The plate 244' is furthermore provided with six through-conductive circuit holes 231-236 which electrically connect together conductive regions located on opposite faces of the plate 244'. The mechanical apertures of the circuit holes are provided on their inner peripheral walls with a layer of deposited copper which is continuous with the copper layer surround- 95 ing each circuit hole at both faces of the plate 244'. The circuit hole 231 electrically con nects lamella 207 with the cross-connecting conductor path 227 and with a soldering land 214 to which the rotor winding 247, 248 will 100 be connected. The circuit hole 232 electrically connects collector lamella 204 with the crossconnecting conductor path 227. The circuit hole 233 electrically connects collector lamella 40 203, as well as the cross-connecting conduc- 105 tor path 228 to a soldering land 215 to which the rotor winding 247, 248 is to be connected. The circuit hole 234 electrically connects collector lamella 201 to the cross-con- necting conductor path 227. The circuit hole 235 electrically connects collector lamella 211 and the cross-connecting conductor path 226 to the soldering land 216 to which the rotor winding 247,248 is to be connected. The cir cuit hole 236 electrically connects collector la- 115 mella 210 to the cross-connecting conductor path 227.

After production of the circuit holes 231 236 and the electrical through-conductive con nections thereof, which conductively connect together the conductive zones surrounding each circuit hole at the two opposite faces of plate 244', say, in the state shown in Fig 21, all conductor paths and lamellas on both faces of the plate 244' are thus now electrically interconnected as required in the final assembly. With the collector plate 244' in this state, firstly the thickness of these metallic components is approximately tripled by galvanic de- position of copper. Then, a thin layer of nickel is galvanically deposited on the copper layer, on both sides of the plate 244'. The best mode is to apply a thin nickel layer only on the surface 230 upon which the brushes actually ride. Thereafter, there is galvanically deposited on the nickel layer a hard gold coating, having a thickness of a few microns, and forming the surface of the collector upon which the brushes actually ride. Finally, the carrier member 244, as shown in Fig 22, is atamped-out from the preliminary plate 244' and provided with a central aperture 276 into which the hub member 245, as shown in Fig 20, is then provided, say, by an injectionmoulding process. As a consequence of such stamping-out of the final carrier member 244, the conductor path 229, needed for the aforementioned galvanic deposition steps, is removed, and the three crossconnecting con- ductor paths 226,227,228 become electrically discontinuous from one another.

Fig 23 depicts the carrier member 244 with six rotor coils secured thereto at its upper face 246. These coils, denoted 247 and 248 in Fig 17 are in Fig 23 denoted X-E' in correspondence to the description of Figs 1 and 3. Starting clockwise from the 1-o'clock position in Fig 23 the sequence of rotor coils is E', D', A', F', C', B'. These circular coils X-E' are, in exactly the same way as in Fig 3, constituted by a single, uninterrupted conductor and provided with similar connection points for connection to collector lamella groups. The connections between individual coils are expressly depicted in Fig 23, as is the winding sense of the coils.

Specifically, the coils A' and B' are connected in series with each other between the soldering lands 216 and 214, namely, between the crossconnecting conductor paths 226 and 227, the coils C' and D' are connected in series with each other between the soldering lands 216 and 215, namely, between the cross-connecting conductor paths 226 and 228, and the coils E' and F' are connected in series with each other between the soldering lands 215 and 214, namely, between the cross- connecting conductor paths 228 and 227.

Further provided is a capacitor module 280 accommodating three deltaconnected capacitors which serve to suppress interference effects. The module 280 is electrically insulating at its underface, at which face it is secured to the carrier member 244, e.g., by cementing. The upper face of the module 280 is provided with three soldering lands, to which, as illustrated, the three connecting points from the three delta-connected coil-pairs A'-B', C'-U, E'-F' are respectively soldered. For example, the connection point 281 between the coils B' and C' extends out to the soldering land 216, soldered thereto, and from there, furthermore, extends to the top one of the three soldering lands on the upper face of the capacitor mo- GB2171854A 10 duie 280, being soldered to the top land. The two other connection points are analogously connected, and their connections expressly shown in Fig 23. The circuit depiction of the connection of the three capacitors to the rotor coils and the collector lamellas is the same as in Fig 2.

The motor of this third embodiment constitutes a particularly small variant of the inven- tion, especially suitable for use in battery powered video recorders, for which application low motor weight is of special importance. Self- evidently, however, the motor of the third embodiment is not limited to such application, nor to the stated dimensions, voltages, etc. In comparison to the motor of the first embodiment, that of the third embodiment has a somewhat inferior efficiency. However, its dimensions are a fraction of those of the motor of the first embodiment and its power about the same. It will be apparent that the form of construction exhibited by the third embodiment is equally applicable to motors where the number of rotor coils, stator poles and/or collector lamellas differs from those illustrated herein, merely for example as shown in Federal Republic of German Offenlegungsschrift DE-OS 32 17 283, the disclosure of which is incorporated herein by reference.

Thus, the structural features exhibited in this third disclosed embodiment of the present invention are to be considered of inventive significance per se.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions and fabrication procedures differing from the types described above.

While the invention has been illustrated and described as embodied in flat-air gap motors having stated numbers of stator poles, rotor coils and collector lamellas, as well as procedures for their fabrication, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the scope of the present invention.

Without further analysis, the foregoing will so fully reveal the concepts of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essen- tial characteristics of the generic or specific aspects of this invention.

Claims (1)

1. A direct-current machine comprising:

(a) a stator including an eight-pole stator 125 magnet arrangement; (b) a six-coil ironless rotor arrangement which is mounted for rotation about a rotor axis and which includes six coils arranged in a single winding layer at equiangular intervals about the rotor axis and a collector arrangement having twelve collector lamellas arranged in a circle about the rotor axis, the angular spacing between corresponding points of suc- cessive lamellas accordingly being substantially 45 mechanical degrees, the twelve collector lamellas consisting of first, second and third collector lamella groups, and each collector lamella group consisting of a resPective four collector lamellas spaced one from the next at angular intervals of 90 mechanical degrees: and (c) means for transmitting current to and from the collector lamellas and for electrically connecting together respective collector lamellas, said means including first and second brush arrangements on the stator electricaliy engaging collector lamellas and angularly offset from each other by about 45 + n X 90 mechanical degrees, wherein n = 0, 1, 2 or 3 and said means further including cross-connecting means operative for causing the four collector lamellas of respective collector lamella groups to be electrically connected to- gether as successive collector lamella groups are electrically engaged by the first and second brush arrangements, wherein the six coils consist of first, second and third coil-pairs, with each coil-pair being con- stituted by two coils located diametrically opposite each other with respect to the rotor axis.

the two coils of each coil-pair are connected in series with each other, and the first, second and third series-connected coilpairs are, respectively, electrically connected between collector lamellas of the first and second collector lamella groups, between collector lamellas of the second and third col- lector lamella groups, and between collector lamellas of the third and first collector lamella groups.

2. A direct-current machine as defined in claim 1, wherein said crossconnecting means comprises first, second and third cross-connecting means provided on the rotor arrangement, with each cross-connecting means permanently electrically connecting together the four collector lamellas of a respective one of the first, second and third collector lamella groups.

3. A direct-current machine as defined in claim 1 or 2, wherein the two coils of each coil-pair are formed of a single conductor means extending without interruption from one coil of the coil-pair to the other coil thereof.

4. A direct-current machine as defined in claim 1,2 or 3 wherein six coils are constituted by conductor means wound without interruption from one coil to the next in such a manner that said conductor means is continuously wound to form the two coils of the first-coil pair and extends without interruption to form the continuously wound two coils of the second coil-pair and the continuously 11 GB2171854A 11 wound two coils of the third coil-pair.

5. A direct-current machine as defined in claim 4, wherein said uninterruptedly-extending conductor means, which constitutes the six coils, includes transitional portions which extend from a coil of one coil-pair to a coil of an adjoining coil-pair, the transitional portions extending first from a coil of one coil pair to a respective connection point and then from that connecting point to a coil of an adjoining coil pair, the so-formed connection points being electrically connected to collector lamellas of respective collector lamella groups.

6. A direct-current machine as defined in claim 5, wherein the transitional portions of said conductor means are inter-coil-pair transitional portions and said uninterruptedly-extending conductor means furthermore include intercoil transitional portions, with the intercoil transitional portions extending from one coil of a respective coil pair to the other coil of the coil pair and the inter-coil transitional portions of said conductor means extending greater distances than do the inter-coil-pair transitional portions of said conductor means.

7. A direct-current machine as defined in any preceding claim, wherein the coils cornprise a cementing or binding lacquer or varnish, whereby the coils are inherently shape- retaining.

8. A direct-current machine as defined in claim 7, wherein the rotor arrangement includes means mounting the coils thereon and mechanically supporting the coils only at por- tions thereof, the remaining portions of the coils extending in free space and being self supporting as a result of their shape-retaining characteristic.

9. A direct-current machine as defined in claim 5 or 6 or claim 7 or 8, when dependent 105 upon claim 5 or 6, wherein each coil is at least approximately symmetrical with regard to a respective symmetry plane passing through the rotor axis, said connection points being spatially located near respective coils but angularly offset relative to the symmetry planes of the respective coils.

10. A direct-current machine as defined in claim 2 or any of claims 3 to 9, when depen- dent upon claim 2, wherein one of said crossconnecting means is spatially located to one side of the collector lamellas.

11. A direct-current machine as defined in claim 10, wherein said one of said cross-con- necting means and the four collector lamellas connected by the latter are respective parts of a one-piece body of an electrically conductive material.

12. A direct-current machine as defined in claim 2 or any of claims 3 to 9, when dependent upon claim 2, wherein one of said crossconnecting means is spatially located to one respective side of the twelve collector lamellas and another of said cross-connecting means is spatially located to an opposite respective side of the collector lamellas.

13. A direct-current machine as defined in claim 12, wherein said one of said cross-connecting means and the four collector lamellas connected thereby are respective parts of a one-piece body of an electrically conductive material, the other of said cross-connecting means and the four collector lamellas connected thereby said respective parts of another one-piece body of an electrically conductive material.

14. A direct-current machine as defined in any of claims 10 to 13, wherein the collector arrangement is generally planar and includes a mounting hub of electrically insulating material for mounting the collector arrangement on the rotor arrangement, one of said cross-connecting means being at least in part located within the mounting hub. 85 15. A direct-current machine as defined in claim 14, wherein the collector arrangement is generally planar and said first, second and third cross-connecting means are formed by respective portions of an electrically conductive material provided on the generally planar collector arrangement, the electrically conductive material of said first, second and third cross-connecting means including respective first, second and third contact portions projecting from the general plane of the collector arrangement, and the rotor arrangement furthermore includes an anti-interference circuit module containing anti-interference circuit components and elec- trically engaged by the first, second and third contact portions.

16. A direct-current machine as defined in claim 15, wherein one of said first, second and third cross-connecting means includes a discrete electrically conductive member which is electrically connected to the lamellas of a respective collector group and is so shaped as to form a spring member maintaining the antiinterference module in electrical engagement with the contact portions.

17. A direct-current machine as defined in claim 16, wherein said discrete electrically conductive member is of a shape including four equiangularly spaced spoke-like portions each of which is in direct electrical engagement with a respective one of the four lamellas of the respective collector lamella group.

18. A direct-current machine as defined in any preceding claim, wherein the stator mag- net arrangement is of a geometry such as to form a planar air gap, through which the stator field of the machine passes, and includes mounting means mounting the coils thereon, said mounting means being mechanically con- nected to and supporting the coils at the portions of the coils located closest to the rotor axis, with the coils extending radially out wardly therefrom in cantilevered fashion into the stator field in the planar air gap.

19. A direct-current machine as defined in 12 GB2171854A 12 claim 18 including a rotor shaft, said mounting means comprising a carrier structure having a generally radially extending portion supporting the coils and an axially extending portion se cured to the rotor shaft, with the collector arrangement being supported on the axially extending portion of the carrier structure.

20. A direct-current machine as defined in any preceding claim, wherein the stator mag net arrangement is of a geometry such as to form a planar air gap and includes two stator magnet arrangements located at opposite axial sides of the planar air gap, the rotor arrange ment including mounting means mounting the coils thereon and the coils extending radially outwardly into the planar air gap.

21. A direct-current machine as defined in claim 20, wherein said mounting means is of generally hexagonal outline, when viewed in the direction of the rotor axis, and has six corner portions, the coils being secured to said mounting means at respective ones of the corner portions.

22. A direct-current machine as defined in any preceding claim, wherein the collector ar- 90 rangement is generally planar and comprises a substrate of an electrically insulating material having thereon a partly etched away thin metallic layer whose remaining portions in clude portions forming the collector lamellas. 95 23. A direct-current machine as defined in claim 22, when dependent upon any of claims 2 to 21, wherein the remaining portions of the thin metallic layer include portions which form at least one of said cross-connecting means. 100 24. A direct-current machine as defined in claim 23, wherein the substrate of electrically insulating material has two major faces of which one face has a partly etched away thin metallic layer thereon, whose remaining por- 105 tions include portions which form the collector lamellas and of which the other face has a partly etched away thin metallic layer whose remaining portions include portions which form one of said cross-connecting means, the por tions of the thin metallic layers which form said cross-connecting means and the collector 33. A method as defined in claim 31 or 32, lamellas, to which said cross-connecting wherein the initial forming step comprises pro means is electrically connected, including in- viding an insulating substrate with a metallic register through-conductive circuit holes on the 115 layer and then etching away portions of the two faces of the substrate. layer to leave remaining portions which consti 25. A direct-current machine as defined in tute the collector lamellas and the cross-con claim 24, wherein the first, second and third necting means and including superfluous por coil-pairs are electrically connected to the con- tions electrically connecting the cross-connect- ductive connecting portions on the other face 120 ing means to collector lamellas other than said of the substrate, thereby being electrically predetermined ones of the collector lamellas, connected to the collector lamellas on the one and utilizing the superfluous portions during face of the substrate. subsequent galvanic deposition of additional 26. A direct-current machine as defined in metallic material on to the remaining portions claim 25, wherein the first, second and third 125 of the metallic layer, and the destroying step coil-pairs are mechanically mounted on the comprises thereafter removing the superfluous other face of the substrate.

27. A direct-current machine as defined in any preceding claim, wherein the stator mag- net arrangement comprises at least one sa- marium-cobalt magnet.

28. A direct-current machine as defined in claim 27, wherein the stator magnet arrangement comprises a circular succession of dis- crete samarium-cobalt magnets, successive ones of the discrete magnets being of alternative polarity.

29. A direct-current machine as defined in any preceding claim, wherein the stator mag- net arrangement comprises a circular succession of discrete stator magnets, successive ones of the discrete stator magnets being of alternate polarity and being spaced from one another by interspaces, with the brush ar- rangements comprising brushes and brush holders holding the brushes and the brush holders being located in interspaces between discrete magnets of the stator.

30. A direct-current machine substantially as hereinbefore described with reference to the accompanying drawings.

31. A method of manufacturing a planargeometry collector having a circular succession of collector lamellas and at least one crossconnecting means which electrically connects together predetermined ones of the collector lamellas to form a collector lamella group, the method comprising initially forming such a collector in which the cross-connecting means electrically connects together collector lamellas in addition to said predetermined ones of the collector lamellas, and then destroying the electrical connection between the cross-connecting means and collector lamellas other than said predetermined ones of the collector lamellas.

32. A method as defined in claim 31, wherein the initial forming step comprises forming a collector blank of sheet metal in which gaps separate the collector lamellas from one another, and the destroying step comprises subsequently providing the collector blank with apertures to render the cross-connecting means discontinuous from collector lamellas other than said predetermined ones of the collector lamellas.

portions.

34. A method as defined in claim 32 or 33, wherein the initial step of forming a collector blank of sheet metal comprises: forming a col- 13 GB 2 171 854A 13 lector blank provided with plural cross-connecting means, each electrically connecting together respective collector lamellas of a respective collector lamellas group; bending-up a portion of each crossconnecting means to form a bent-up conductive contact tab; and embedding at least portions of the collector blank in electrically insulating material which envelops the bent-up conductive contact tabs, except for the free end portions of the tabs.

35. A method of manufacturing a planargeometry collector for a directcurrent machine substantially as hereinbefore described.

36. A method of using the machine as de- fined in any of claims 1 to 30, comprising using said machine as a drive motor for driving a capstan in a signal-recording or reproducing apparatus.

37. A signal-recording or reproducing appa- ratus incorporating a direct-current machine as defined in any of claims 1 to 30, for use as a drive motor of a capstan thereof.

38. A planar-geometry collector for a directcurrent machine when manufactured by a method as defined in any of claims 31 to 35.

Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1986. 4235. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.