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(11) | EP 0 133 802 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
A rotary transformer Ein rotierender Transformator Un transformateur tournant |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to an improvement in a rotary transformer and, in particular, relates an improvement in the structure of a pair of identical disc cores made of ferro-magnetic material.
[0002] A rotary transformer is generally used to couple electrically a rotating component and a stationary component in a magnetic storage apparatus such as a video tape recorder (VTR).
[0003] A conventional multi-channel rotary transformer will be described in more detail subsequently and comprises a pair of identical disc cores which are mounted for relative rotation, each of the disc cores comprising a number of concentric annular grooves provided on the facing surfaces for accommodating coils, each of the annular grooves being concentric with the centre of the disc core and having a first hole for lead wires from the coil.
[0004] According to this invention in such a rotary transformer each of the annular grooves of each disc core has a second hole of the same configuration as the first hole, the second hole being positioned diammetrically opposite the first hole, and the first and second holes being symmetrically located with regard to the centre of the disc core so that the disc core is balanced.
[0005] Preferably a recess is provided in each annular projection located between two adjacent annular grooves the recess being located adjacent a hole and extending across the entire width of the annular projection.
[0006] Particular examples of rotary transformers in accordance with this invention will now be described and contrasted with conventional rotary transformers with reference to the accompanying drawings ; in which :
Figure 1 is a cross-section through a conventional transformer ;
Figure 2(A) is a plan of a conventional disc core ;
Figure 2(B) is a cross-section taken along the line A-A shown in Figure 2A ;
Figure 3 is a plan of a disc core used in a first example of rotary transformer in accordance with the present invention ;
Figure 4 is a plan of a disc core used in a second example of rotary transformer in accordance with the present invention ;
Figure 5(A) is a plan of a disc core used in a third example of rotary transformer in accordance with the present invention ;
Figure 5(B) is a scrap, partly sectional, enlarged perspective view of the third example ;
Figure 6 is a plan of a disc core used in a fourth example of rotary transformer in accordance with the present invention.
[0007] Figure 1 is a cross-sectional view of prior rotary transformer of four channel type. In this figure, a rotor 12 is fixed to a shaft 10 rotated by an electric motor (not shown). A disc rotor core 14 made of ferro-electric material such as ferrite is fixed to the bottom surface of the rotor 12 by adhesive means. On the surface of the rotor core 14 opposite to the surface to which the rotor 12 is fixed, five annular grooves 16 which are coaxial with the longitudinal axis of the shaft 10 respectively, are provided. Coils 18 are accommodated in four annular grooves of five, respectively. A disc stator core 20 having coils 24 accommodated in annular grooves 22, which is the same structure as the rotor core 14, is fixed to the inner surface of a case 26 fixed to the body of a VTR so that the annular grooves 16 of the rotor core 14 is opposite to ones 22 of the stator core 20 with a predetermined spacing.
[0008] Figure 2(A) is a plan view of the disc rotor core 14 of Figure 1, which is the same structure as the disc stator core 20, and Figure 2(B) is a cross-sectional view along the line A-A of Figure 2 (A). The annular grooves 141 - 145 are arranged on the surface of the disc core 14 so that they are concentric with the centre C of the disc core 14 respectively. As a result, annular projections 281 - 285, which are also concentric with the centre C, are formed on the same surface of the disc core 14.
[0009] Coils are accommodated in the grooves 161, 162, 164 and 165, respectively. An annular short ring (not shown) is embedded in the groove 163 in order to separate magnetically coils accommodated in each of the grooves 161, 162 from coils in each of the grooves 164, 165. The annular grooves 161, 162, 164 and 165 have through holes 301, 302, 304 and 305, respectively, each of the through holes being in the cylindrical shape and coupling the bottom surface of the groove with the bottom surface of the disc core 14. Lead wires 32 from the coils are extended through the holes 30 to the bottom surface of the disc core 14 on which no grooves are provided, and are connected to an external circuit (not shown).
[0010] The disc core hereinabove is produced by ferromagnetic material such as ferrite through molding process, sintering process and finish process.
[0011] In operation of the rotary transformer having a pair of the disc cores above-mentioned, the rotor core 14 is rotated, on the other hand the stator core 20 is held stationary. Each signal in the coils of the rotor core 14 is magnetically transferred to the corresponding coil of the stator core 20, vice versa.
[0012] However, the prior rotary transformer has the following disadvantages.
(1) In general, the through holes of the disc core are arranged so as to be close to one another as shown in Figure 2(A) in order to facilitate the operation of extending the lead wires through the through holes to the bottom surface of the disc core. Thus, the presence of the through holes causes the unblanaced of mass of the disc core. That is, the equilibrium point in mass of the disc core is not at the centre C of the disc core. Therefore, the unbalanced of mass of the disc core results in non-uniformity of rotary motion of the disc core such as run-out when the disc core rotates. In particular, non-uniformity of rotary motion of the disc core is more remarkable when the disc core rotates at high speed or when the external diameter of the disc core is large ; such a disc core is used to the rotary transformer of multi-channel type such as four or five channel type. Further, non-uniformity of rotary motino affects electric and/or magnetic characteristics of the rotary transformer.
(2) As mentioned above, shaping of the disc core is attained by molding process in which ferromagnetic material of powder type is pressed by means of an upper punch having projections corresponding to the grooves and the through holes of the disc core, and a lower punch having flat surface corresponding to the flat bottom surface of the disc core. In this molding process, referring to Figure 2, a portion 34, of the annular projection 282 between the adjacent through holes 301 and 302 is not pressed strongly enough to attain given compressibility of ferromagnetic material of power type. Thus, the portion 341 of the disc core molded is mechanically weak compared with the other portions of the disc core and is apt to be cracked or broken. Also, even if there is no undesirable cracking or breakage at the portion 34, of the disc core at the molding process stage, they may generate at the portion 34, of the disc core at the sintering process. It will be apparent that cracking or breakage may generate at a portion 342 of the annular projection 285 between the adjacent through holes 304 and 305. Also, when the width of the annular projection is relatively small (for example, smaller than 0.8mm), similar cracking or breakage will generate at portions 36, and 362 adjacent to the through holes 301 and 305, respectively. Cracking or breakage generates in spite of the kind of ferromagnetic material. Therefore, yield rate on the process for producing the core of Figure 2 is low.
[0013] The rotary transformer according to the present invention comprises a pair of improved identical disc cores arranged so that relative rotary motion is established as shown in Figure 1, and the present improved disc core is shown in Figure 3, in which identical numerals denote identical elements in Figure 2. The principle feature of the present invention is the presence of second through holes, or dummy through holes 28 for compensating the unbalance of mass of the prior disc core 14 resulting from the resence of the first through holes 30. The second through holes 381, 382, 384 and 385 are positioned in the annular grooves 161, 162, 164 and 165 respectively so that the first through holes 30 and the second through holes 38 are symmetrical with regard to the centre C of the disc core 14. In detail, the through holes 30, and 381; 302 and 382; 304 and 384; 305 and 385 are symmetrical with regard to the centre C of the disc core 50, respectively. Each of the second through holes 38 is the same structure as each of the first through holes 30. Therefore, each of the second through holes 38 is in the cylindrical shape and couples the bottom surface of the grooves 16 with the bottom surface of the disc core 14. Of course, the shape of the first through holes 30 and the second through holes 38 is not limited to the cylindrical one, and thus, various shapes can be designed.
[0014] The disc core 50 of Figure 3 is produced by ferromagnetic material such as ferrite through molding process, sintering process and fiishing process. In particular, the second through holes 38 are shaped preferably together with the first through holes 30 by means of a molding process.
[0015] The rotary transformer according to this embodiment is assembled, similar to Figure 1, using a pair of the present disc cores. With a transformer in accordance with the present invention, it will be apparent that uniform rotary motion can be established because of the presence of the second through holes 38 for compensating unbalance of mass of the disc resulting from the presence of the first through holes 30. Further, according to the embodiment, the lead wires to be connected to an external circuit can be extended through either the first through holes 30 or the second through holes 38. Thus, greater flexibility in the arrangement of the lead wires is obtained compared with the disc core of Figure 2.
[0016] Figure 4 shows a further improved disc core 60 utilized in the present rotary transformer, in which the feature of the present disc core is the presence of third through holes 40 and fourth through holes 42. The third and the fourth through holes 40, 42 are arranged in the grooves 16 so that they lie near the line C-C perpendicular to the line B-B near which the first and the second through holes 30, 38 lie. Further, the third through holes 40 and the fourth through holes 42 are positioned so that the third through holes 40 and the fourth through holes 42 are symmetrical with regard to the centre C of the disc core 14. Each of the third and the fourth through holes is the same structure as each of the first and the second through holes 30, 38. The presence of the third and the fourth through holes 40, 42 is to overcome the disadvantage of the disc core of Figure 3. That is, when the external diameter of the disc core of Figure 3 is large, it has been observed that the shape of the molded disc core in the cross section along the line perpendicular to the line B-B of Figure 3 is apt to be deformed in V-shaped structure. According to the disc core of Figure 4, in which the third through holes 40 and the fourth through holes 42 lie near the line C-C perpendicular to the line B-B, it has been observed that degree of deformation in V-shaped structure decreases. Thus, the disc core of Figure 4 is useful when its external diameter is large. Further, the present disc core has an advantage that extending operation of the lead wires can be more facilitated compared with the disc core of Figure 3.
[0017] Figure 5(A) is a plan view of a further improved disc core 70 utilized in the present rotary transformer, and Figure 5(B) is an enlarged perspective view, partly in cross section along the line D-D of Figure 5(A). The feature of the present disc core 70 is the presence of recesses 44 for preventing generation of cracking or breakage which will appear at portions of the annular projections 28 between two adjacent through holes 301 and 302; 304 and 305; 381 and 382; 384 and 385.
[0018] In Figure 5(B), there is provided a recess 441 at a portion of the annular projection 282 between two adjacent through holes 301, 302 (in this Figure, the half of the recess 441 and the half of each of the holes 301, 302 are shown). The recess 441 couples both the side walls of the annular projection 282. The bottom surface of the recess 441 is generally parallel to the bottom surface of the disc core 70 and the opposite side walls of the recess 441 are generally parallel to each other. The edges of the recess 441 may be rounded off. The depth D1 of the recess 441 is designed so as to be equal or smaller than the depth D2 of the annular grooves 16. The width W1 of the recess 441 is designed so as to be nearly equal to the diameter of the through holes 301, 302. Of course, another recesses 442, 444 and 445 are designed in the same manner as the recess 441. The size of those recesses 44 is practically selected depending on the diameter of the through holes 30, the width W2 of the annular projections 28 and the thickness T1 of the disc core 14. For example, when the thickness T1 is in the range from 1.5 to 4.0 mm and the depth D2 of the grooves 16 is nearly equal to 0.6 mm, and the depth D1 of the recesses 44 is set to be equal to 0.1 - 0.2 mm and the width W1 is set to be nearly equal to the diameter of the through holes 30, 38.
[0019] The forming of the disc core of Figure 5 is achieved by the molding process in which ferromagnetic material of powder type is pressed by an upper punch comprising projections, corresponding to the recesses 44 and a lower punch including the surface corresponding to the flat bottom surface of the disc core. It has been observed that no cracking or breakage is generated in the disc core when the recesses 44 are included.
[0020] Figure 6 shows a still further improved disc core 80 utilized in the present rotary transformer. This disc core further comprises recesses 46 in addition to the recesses 44 of the disc core 70 of Figure 5. The recesses 46 are provided at portions of the annular projections adjacent to one of the through holes. That is, the recesses 461, 463 are provided at portions of the annular projection 281 adjacent to the through holes 301, 381 respectively, and the recesses 462, 464 are provided at portions of the annular projection 286 adjacent to the through holes 305, 385 respectively. The recesses 46 prevent generation of cracking or breakage at the projections 281, 286. The disc core of Figure 6 is useful when the width of the annular projections is relatively small.
1. A multi-channel rotary transformer comprising a pair of identical disc cores (50,
60, 70, 80) which are mounted for relative rotation, each of the disc cores (50, 60,
70, 80) comprising a number of concentric annular grooves (161, 162, ... 165) provided on the facing surfaces for accommodating coils (18, 24), each of the annular
grooves (161, 162, ... 165) being concentric with the centre of the disc core (50, 60, 70, 80) and having a
first hole (301, 302, ... 305) for lead wires from the coil, characterised in that each of the annular grooves
(161, 162, ... 165) of each disc core (50, 60, 70, 80) has a second hole (381, 382, ... 385) of the same configuration as the first hole (301, 302, ... 305), the second hole (381, 382, ... 385) being positioned diammetrically opposite the first hole (301, 302, ... 305), and the first (301, 302, ... 305) and second (381, 382, ... 385) holes being symmetrically located with regard to the centre of the disc core (50,
60, 70, 80) so that the disc core (50, 60, 70, 80) is balanced.
2. A rotary transformer according to claim 1, wherein each of the first (301, 302 ... 305) and second (381, 382, ... 385) holes is cylindrical.
3. A rotary transformer according to claim 1 or 2, wherein a recess (441, 442, ... 444) is provided in each annular projection (282, 283, ... 285) located between two adjacent annular grooves (161, 162, ... 165) the recess (441, 442, ... 444) being located adjacent a hole (3091, ... 305; 381, ... 385) and extending across the entire width of the annular projection (282, 283, ... 285).
4. A rotary transformer according to the claim 3, wherein the recess (441, 442, ... 444) is substantially rectangular in shape, the depth (D1) of the recess (441, 442, ... 444) being equal to or lower than that (D2) of the annular grooves (161, 162, ... 165) and the width (W) of the recess (441, 442, ... 444) being equal to the diameter of the first (301, 302, ... 305) and second (381, 382, ... 385) holes.
1. Vielfachkanal-Rotationswandler mit einem Paar von identischen Plattenkernen (50,
60, 70, 80), die zur relativen Rotation montiert sind, wobei jeder der Plattenkerne
(50, 60, 70, 80) eine Anzahl von konzentrischen, ringförmigen Nuten (161, 162, ... 165) umfaßt, die auf Stirnoberflächen zur Aufnahme von Spulen (18, 24) vorgesehen sind,
wobei jede der ringförmigen Nuten (161, 162, ... 165) konzentrisch ist zu dem Zentrum des Platten kerns (50, 60, 70, 80) und ein erstes
Loch (301, 302, ... 305) für Leitungsdrähte von der Spule aufweist, dadurch gekennzeichnet, daß jede der
ringförmigen Nuten (161, 162, ... 165) von jedem Plattenkern (50, 60, 70, 80) ein zweites Loch (381, 382, ... 385) von derselben Konfiguration wie das erste Loch (301, 302, ... 305) hat, wobei das zweite Loch (381, 382, ... 385) diametral gegenüber dem ersten Loch (301, 302, ... 305) angeordnet ist, und die ersten (301, 302, ... 305) und zweiten (381, 382, ... 385) Löcher in bezug auf das Zentrum des Plattenkerns (50, 60, 70, 80) symmetrisch so
angeordnet sind, daß der Plattenkern (50, 60, 70, 80) ausbalanciert ist.
2. Rotationswandler nach Ansprung 1, bei dem jedes der ersten (301, 302, ... 305) und zweiten (381, 382, ... 385) Löcher zylindrisch ist.
3. Rotationswandler nach Anspruch 1 oder 2, bei dem eine Ausnehmung (441, 442, ... 444) in jedem ringförmigen Vorspruch (282, 283, ... 285), der zwischen zwei benachbarten ringförmigen Nuten (161, 162, ... 165) angeordnet ist, vorgesehen ist, wobei die Ausnehmung (441, 442, ... 444) an ein Loch (301, ... 305; 381, ... 385) angrenzend angeordnet ist und sich quer über die gesamte Breite des ringförmigen
Vorsprungs (282, 283, ... 285) erstreckt.
4. Rotationswandler nach Anspruch 3, bei dem die Ausnehmung (441, 442, ... 444) im wesentlichen eine rechtwinklige Form hat, die Tiefe (D1) der Ausnehmung (441, 442, ... 444) gleich oder geringer als diejenige (D2) der ringförmigen Nuten (161, 162, ... 165) ist und die Breite (W) der Ausdehnung (441, 442, ... 444) gleich dem Durchmesser der ersten (301, 302, ... 305) und zweiten (381, 382, ... 385) Löcher ist.
1. Transformateur tournant à plusieurs canaux comprenant deux noyaux plats identiques
(50. 60, 70, 80) montés en vue de tourner l'un par rapport à l'autre, chacun des noyaux
plats (50, 60, 70, 80) présentant un certain nombre de rainures annulaires concentriques
(161, 162, ... 165) ménagées dans les surfaces se faisant face pour recevoir des enroulements (18, 24),
chacune des rainures annulaires (161, 162, ... 165) étant centrée sur le centre du noyau plat (50, 60, 70, 80) et présentant un premier
trou (301, 302, ... 305) de réception de fils partant de l'enroulement, caractérisé en ce que chacune des
rainures annulaires (161, 162, ... 165) de chaque noyau plat (50, 60, 70, 80) présente un second trou (381, 382, ... 385) de même configuration que le premier trou (301, 302, ... 305), le second trou (381, 382, ... 385) étant diamétriquement opposé au premier trou (301, 302, ... 305), et les premiers (301, 302, ... 305) et seconds (381, 382, ... 385) trous étant placés symétriquement par rapport au centre du noyau plat (50, 60, 70,
80) de façon que le noyau plat (50, 60, 70, 80) soit équilibré.
2. Transformateur tournant selon la revendication 1, dans lequel chacun des premiers
(301, 302, ... 305) et seconds (381, 382, ... 385) trous est cylindrique.
3. Transformateur tournant selon la revendication 1 ou 2, dans lequel un évidement
(441, 442, ... 444) est prévu dans chaque saillie annulaire (282, 283, ... 285) située entre deux rainures annulaires (161, 162, ... 165) voisines, l'évidement (441, 442, ... 444) étant situé près d'un trou (301, ... 305; 381, ... 385) et s'étendant de part en part de la largeur de la saillie annulaire (282, 283, ... 285).
4. Transformateur tournant selon la revendication 3, dans lequel l'évidement (441, 442, ... 444) est de forme sensiblement rectangulaire, la profondeur (D1) de l'évidement (441, 442, ... 444) étant égale ou inférieure à celle (D2 des rainures annulaires (161, 162, ... 165) et la largeur (W) de l'évidement (441, 442, ... 444) étant égale au diamètre des premiers (301, 302, ... 305) et seconds (381, 382, ... 385) trous.