Motor armature and method of formation

Abstract: A motor armature which facilitates assembly and miniaturisation, comprises an inner cylinder 1 coaxial with an outer cylinder 2 and a plurality of pole pieces 3 provided radially at equal intervals between the inner cylinder 1 and the outer cylinder 2. The inner cylinder 1 is formed into a cylindrical shape by bending in the longitudinal direction a hoop member (band steel) made of a magnetic material and having a predetermined thickness and length. The outer cylinder 2 is made of the hoop member similarly to the inner cylinder 1. Each pole piece 3 comprises a coil 4 wound around a wire piece 5 obtained by cutting a wire (wire rod) made of a magnetic material and having a predetermined thickness and length, one end of the wire piece 5 being fixed to the outer peripheral face of the inner cylinder 1 by means of welding and the other end of the wire piece being fixed to the inner peripheral face of the outer cylinder 2.

Description: The present invention relates to a motor armature particularly, though not exclusively for use in motors such as a brushless motor, and a manufacturing method thereof. Armatures used for a brushless motor are known, either fabricated by winding a coil around an iron core made by laminating a plurality of punched steel plates, or fabricated by winding a coil around an iron core made by laminating a plurality of punched steel plates which are divided into a plurality of pieces and by cylindrically connecting each core around which the coil is wound. However, in the former case, the armature fabricated by winding the coil around the iron core made by laminating a plurality of punched steel plates has had problems that its overall structure is complicated and that it is difficult to wind the coil around the core. In the latter case, the armature fabricated by winding the coil around the iron core made by laminating a plurality of punched steel plates which are divided into a plurality of pieces and by cylindrically connecting each core around which the coil is wound has had a problem that although it is easy to wind the coil around the core, the assembly work thereof for connecting cylindrically each core piece around which the coil is wound is difficult. GB 0217597 discloses a magneto-electric machine for lighting a bicycle in which an armature comprises a plurality of pole pieces each comprising a coil wound around a rod formed of magnetic material. The pole pieces are attached to extend radially from one side of a cylinder formed of magnetic material. US 5481143 discloses a self starting brushless dc motor having a stator assembly which comprises a circular ring member and a plurality of electromagnets positioned around the circular ring member. SUMMARY OF INVENTION Accordingly, it is an object of the present invention to provide a motor armature whose assembly can be facilitated. In a first aspect, this invention provides motor armature, comprising: a plurality of pole pieces each comprising a coil wound around a rod formed of a magnetic material; and characterised by further comprising: concentrically disposed first and second cylinders formed of bands of magnetic material, with said plurality of pole pieces extending therebetween and being fixed to both cylinders. In a second aspect, this invention provides a method for manufacturing a motor armature, comprising: a step of creating a plurality of pole pieces in each of which a coil is wound around a rod made of a magnetic material; and characterised by further comprising: a step of fixing one end of each of said plurality of pole pieces to the inner peripheral face of a first cylinder and the other end of each said plurality of pole pieces to the outer peripheral face of a second concentric inner cylinder, wherein said cylinders are formed by bending a band member of a magnetic material. A motor armature of the present invention comprises a plurality of pole pieces in which a coil is wound around a rod made of a magnetic material; and tubular concentric cylinders made of a magnetic material which have affixed between them the plurality of pole pieces disposed radially at equal intervals at the position distant from the centre by a predetermined distance. The above-mentioned cylinders are formed by curling up or bending a hoop, band, or strip member made of a magnetic material and the rod is a wire piece obtained by cutting a wire made of a magnetic material. Because the armature of the present invention is simply constructed as described above, it facilitates assembly and miniaturisation, thinning and reduction of cost. Further, it allows changes in the size and structure of the armature readily and swiftly implemented. A method for manufacturing the motor armature of the invention comprises a first step of creating a plurality of pole pieces in which a coil is wound around a wire piece made of a magnetic material; a second step of fixing one end of the plurality of pole pieces created in the first step to one and the same plane of a hoop member made of a magnetic material at equal intervals; and a third step of creating a cylinder attached with pole pieces by curling up the hoop member to which the plurality of pole pieces are fixed in the second step so that the plurality of pole pieces come inside or outside. Further, in parallel with creating the cylinder attached with the pole pieces by curling up the hoop member to which the plurality of pole pieces are attached so that the plurality of pole pieces come outside, in the third step described above, an outer cylinder is created while fixing each other end of the pole pieces with the hoop member. Further, an inventive method for manufacturing the motor armature comprises a first step of creating a plurality of pole pieces in which a coil is wound around a wire piece made of a magnetic material; and a second step of fixing one end of the plurality of pole pieces created in the first step either to the inner peripheral face or the outer peripheral face of a cylinder formed by curling up a hoop member made of a magnetic material radially at equal intervals. Further, in the second step described above, an outer cylinder is arranged coaxial with the cylinder attached with the pole pieces and fixed with the other end of the plurality of pole pieces fixed to the cylinder attached with the pole pieces after creating the cylinder attached with the pole pieces by curling up the hoop member so that the plurality of pole pieces come outside. Thus, the rod (wire piece) and the hoop members are used in the inventive method for manufacturing the armature. It then allows the automation to be facilitated and to deal with changes in the size and structure of the armature swiftly by changing the thickness of the wire piece and the thickness of the hoop member. BRIEF DESCRIPTION OF DRAWINGS Preferred embodiments of the invention will now be described with reference to the accompanying drawings, wherein: FIG. 1 is a perspective view showing an embodiment of an armature of the present invention. FIG. 2 is a perspective view showing a structure of a pole piece of Figure 1. FIG. 3 is a section view showing a section of the wire piece of Figure 2. FIG. 4 is a magnetic characteristic chart of magnetic materials. FIG. 5 is a frequency characteristic chart of the magnetic materials. FIG. 6 is a frequency characteristic chart of permeability. FIG. 7 is a drawing showing steps of a first method for manufacturing of the armature in accordance with the invention. FIG. 8 is a drawing showing a method for creating the pole piece. FIG. 9 is a drawing showing another method for creating the pole piece. FIG. 10 is a drawing diagrammatically showing a coil winding machine. FIG. 11 is a drawing showing steps of a second method for manufacturing of the armature in accordance with the invention. FIG. 12 is a drawing showing steps of a third method for manufacturing of the armature in accordance with the invention. FIG. 13 is a drawing showing steps of a fourth method for manufacturing of the armature in accordance with the invention. FIG. 14 is a drawing showing steps of a fifth method for manufacturing of the armature in accordance with the invention. FIG. 15 is a section view showing a spindle motor having a motor armature as shown in FIG. 1. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view of the preferred armature according to the invention, and, as shown in FIG. 1, the armature is constructed by disposing coaxially an inner cylinder 1 and an outer cylinder 2 and by providing a plurality of pole pieces 3 radially at equal intervals between the inner cylinder 1 and the outer cylinder 2. The inner cylinder 1 is formed into the cylinder shape by curling up or bending in the longitudinal direction a band or hoop member of steel which is made of a magnetic material and which has a predetermined thickness and length and by jointing the both ends thereof by welding or the like. Similarly to the inner cylinder 1, the outer cylinder 2 is formed into the cylinder shape by bending in the longitudinal direction a band or hoop member of steel which is made of a magnetic material and which has a predetermined thickness and length and by jointing the both ends thereof by welding or the like. As shown in Fig. 2, the pole piece 3 consists of a wire piece 3 obtained by cutting a wire (wire rod) which is made of a magnetic material and which has a predetermined thickness into a predetermined length and a coil 4 wound around the wire piece 5. One end of the wire piece 5 is fixed to the outer peripheral face of the inner cylinder 1 by welding or the like and the other end of the wire piece 5 is fixed to the inner peripheral race or the outer cylinder 2. While the plurality of pole pieces 3 are provided between the inner cylinder 1 and the outer cylinder 2, the number thereof is determined depending on a design and specifications of a motor, like three, six, eight, nine or twelve. Because the wire piece 5 is obtained by cutting a wire and its shape of section is the same (circular) in the longitudinal direction, there is a merit that the coil 4 can be readily wound by a coil winding machine. However, the shape of the wire piece 5 is not limited only to such shape, and it is possible to provide fixing sections like convex sections at the both ends thereof so as to insert the convex sections to fixing holes provided on the inner cylinder 1 and the outer cylinder 2, Further, the sectional shape of the wire piece 5 in the longitudinal direction is not limited to be circular, and it may be triangular or square. Still more, the wire piece 5 may be formed by laminating thin plate-like members. The internal structure of the wire piece 5 will now be explained with reference to FIG. 3. The wire piece 5 is composed of a centre layer 5A whose section is circular and a skin layer 5B which is formed so as to have a constant thickness around the centre layer 5A. The centre layer 5A is made of low carbon steel or pure iron which are magnetic materials having high saturation magnetic flux density. The skin layer 5B is made of Fe-Co alloy, Fe-Ni alloy or amorphous alloy which are magnetic materials having high magnetic permeability and causing less iron loss. The reason why the wire piece 5 is composed of the two layers, using the magnetic materials having different natures, will be explained below. FIG. 4 is a magnetic characteristic chart of various magnetic materials. FIG. 5 is a frequency characteristic chart of iron loss the magnetic materials. FIG. 6 is a frequency characteristic chart of permeability of the magnetic materials. According to FIG. 4, when the strength of magnetic field is determined in order of a, b, c, d and e, the flux density corresponding to that is determined accordingly. When the armature of the present mode is used in a motor, there is no big difference in the iron loss of the various magnetic materials in activating the motor because alternating frequency is low as shown in FIG. 5. Accordingly, the pure iron and silicon steel which can be readily worked are suited. Further, because a large torque is required in activating the motor and a large current flows through the coil, increasing the strength of the magnetic field, the pure iron and the silicon steel which are the magnetic materials having the high saturation magnetic flux density as shown in FIG. 4 are suited. When the motor rotates at high speed after the activation on the ether hand, the alternating frequency of the magnetic flux becomes high. In this case, although the iron loss of the pure iron and the like increases remarkably in correspondence to the increase of the frequency, the iron loss of the amorphous alloy and the like does not increase so much in correspondence to the increase of the frequency, the Fe-Co alloy, Fe-Ni alloy or amorphous alloy is suited. Further, as the strength of the magnetic field is reduced because the current flowing through the coil decreases during the high speed rotation of the motor after the activation, the one having relatively high saturation magnetic flux density is suited, even though the strength of the magnetic field is small like the Fe-Co alloy, Fe-Ni alloy or amorphous alloy as shown in FIG. 4. Thus, the magnetic materials suited as the wire piece 5 are mutually contradictory in activating the motor and in rotating it at high speed after the activation and it is difficult to cover the whole range from the activation to the high speed rotation of the motor by either one of the magnetic materials. Therefore, it is conceivable to combine the two materials having the different natures. During the high speed rotation of the motor after the activation, the alternating frequency of the magnetic flux is high so that it causes a skin effect of the magnetic flux. As result, the magnetic flux density of the wire piece 5 on the skin side increases so that the wire piece 5 is caused less iron loss at the centre side thereof and caused large iron loss at the skin side thereof. Accordingly, it is preferable to make the skin side of the wire piece 5 by the Fe-Co alloy, Fe-Ni alloy or amorphous alloy which causes less iron loss even when the frequency is high as shown in FIG. 5 in order to minimise the large iron loss at the skin side caused by the skin effect. It is preferable to make the centre layer 5A of the wire piece 5 by the low carbon steel or pure iron which are the magnetic materials having high saturation magnetic flux density and to make the skin layer 5B by the Fe-Co alloy, Fe-Ni alloy or amorphous alloy which are the magnetic materials having high magnetic permeability and causing less iron loss. By composing the wire piece 5 as described above, a loss caused by the iron loss may be reduced across the whole range from the activation to the high speed rotation of the motor. It also allows a magnetic flux necessary for driving to be obtained mainly by the centre layer 5A part in activating the motor and a magnetic flux necessary for rotation to be obtained mainly by the skin part 5B in rotating the motor at high speed. Further, the iron loss caused by the skin effect of the magnetic flux may be reduced even if a number of rotation of the motor is increased from several thousands rpm to ten thousands rpm by composing the wire piece 5 as described above. The armature of the present embodiment constructed as described above may be used by combining either an inner rotor or an outer rotor made of permanent magnet for example. Further, the armature may be modified in that the outer cylinder 2 is removed from the armature shown in FIG. 1 (armature which is composed of the pole pieces 3 and the inner cylinder 1). The armature of the present invention may also be modified in that the inner cylinder 1 is removed from the armature shown in FIG. 1 (armature which is composed of the pole pieces 3 and the outer cylinder 2). In these cases, the armature is used by combining with an inner or outer rotor respectively. Methods for manufacturing the armature constructed as described above will be explained below. FIG. 7 is a process drawing for explaining a first method for manufacturing the armature. In the first manufacturing method, the coil 4 is wound as described later around the wire pieces 5 which are obtained by cutting a wire made of a magnetic material into a predetermined length to create the plurality of pole pieces 3 as shown in FIG. 7(A). Here, six pole pieces 3 are created. Next, one end of the wire piece 5 of the plurality of pole pieces 3 is fixed to a hoop member 11 which has been cut into a predetermined length beforehand at equal intervals by joint means such as spot welding or caulking as shown in FIG. 7 (B). Then, in parallel with creating the inner cylinder by winding the hoop member 11 around a core 12, each of the other end of the wire piece 5 of the pole pieces 3 is fixed to a hoop member 13 by means of spot welding or caulking to create the outer cylinder as shown in FIG. 7 (C). Then, the armature as showing FIG. 1 is completed. It is noted that in FIG. 7(C), the inner cylinder may be created in advance by curling up the hoop member 11 on which the pole pieces 3 are fixed and the outer cylinder may be created thereafter by curling up the hoop member 13 as described above. It is noted that although the pole piece 3 is created by winding the coil 4 around the wire piece 5 which has been cut in advance in FIG. 7(A), it is also possible, instead of that, to wind the coil 4 at the edge of the continuous wire in advance and to cut the wire into the length of the wire piece 5 after winding the coil 4. Further, although the one end of the pole piece 3 is fixed to the hoop member 11 which has been cut in advance in FIG. 7(B), it is also possible instead of that, to fix one end of the plurality of pole pieces 3 to the hoop member 11 and to cut the hoop member after finishing the fixation. Next, a method for creating the pole pieces 3 by winding the coil around the wire piece explained in FIG. 7(A) will be explained. FIG. 8 is a drawing diagrammatically showing a case of creating a three-phase coil by using three coil winding machines. In this case, the winding directions of the six pole pieces are all the same. Then, star connection or delta connection is made after that. FIG. 9 is a drawing diagrammatically showing a case of creating the three-phase coil by using one coil winding machine. In this case, the three poles of each phase of A, B and C are wound forward, backward and forward. A delta connection is made by hooking two spots to connect the beginning and the end of the winding as shown in FIG. 9. FIG. 10 is a drawing diagrammatically showing a coil winder 20 for winding the coil 4 around the wire piece 5. This coil winder 20 comprises a cylindrical base 21, a cylindrical winding section 22 which continues therefrom and bifurcates to the left side of the figure and a balance section 23 which bifurcates to the right side of the figure. It is constructed so that the whole of it moves forward and back while turning. In winding the coil 4 around the wire piece 5, the coil 4 is discharged from an opening at the edge of the winding section 22 via the base 21 and the winding section 22 and the whole coil winder 20 moves forward or back while turning. Thereby, the discharged coil 4 is wound around the wire piece 5. It is noted that the balance section 23 takes a balance when the winding section 22 turns. The rotation speed of the coil winding machine is around 3000 rpm at most in winding a coil around a prior art armature by means of the special coil winding machine because the structure of the armature is complicated. However, the wire piece 5 of the present mode is a rod whose section is circular in the longitudinal direction, there is a merit that the number of rotation of the coil winding machine may be increased up to 50,000 to 60,000 rpm in winding the coil 4 by the above-mentioned coil winding machine. A second method for manufacturing the armature will now be explained with reference to process drawings shown in FIG. 11. The second manufacturing method is the same with the first manufacturing method up to the steps of creating the plurality of pole pieces 3 in which the coil 4 is wound around the wire piece 5 and of fixing one end of the wire piece 5 of the plurality of pole pieces 3 to the hoop member 11 at equal intervals (see Figs. 11(A) and 11(B)). When the hoop member 11 is curled up by winding around the core and the both ends thereof are jointed by welding or the like, the inner cylinder 1 on which the pole pieces 3 are disposed radially is created as shown in FIG. 11(C). When the outer cylinder 2 made of the hoop member is disposed coaxially with the inner cylinder 1 as shown in FIG. 11 (D), the inner peripheral face of the outer cylinder 2 contacts with each other end of the wire piece of the pole piece 3. Each other end of each wire piece is then jointed with the inner peripheral face thereof by means of spot welding or the like, thus completing the armature as shown in FIG. 1. The armature thus created by the second manufacturing method may be used in combination either with an inner rotor or an outer rotor. The armature in the state in FIG. 11(C) may be used in combination with the outer rotor. A third method for manufacturing the armature will now be explained with reference to process drawings shown in FIG. 12. The third manufacturing method is the same with the first manufacturing method up to the steps of creating the plurality of pole pieces 3 in which the coil 4 is wound around the wire piece 5 and or fixing one end of the wire piece 5 of the plurality of pole pieces 3 at equal intervals to a hoop member 14 cut into a predetermined length in advance (see Figs. 12 (A) and 12(B)). When the hoop member 14 is curled up by winding around the core so that each pole piece 3 comes inside and the both ends thereof are jointed by welding or the like, a cylinder in which the pole pieces 3 are fixed so as to head the centre is created as shown in FIG. 12 (C) . Thus, the armature which can be used in combination with the inner rotor is completed. A fourth method for manufacturing the armature will now be explained with reference to process drawings shown in FIG. 13. The fourth manufacturing method is the same with the first manufacturing method up to the step of creating the plurality of pole pieces 3 in which the coil 4 is wound around the wire piece 5 (see FIG. 13(A)). One end of the wire piece 5 of the plurality of pole pieces 3 is fixed radially at equal intervals to the outer peripheral face of the inner cylinder 1 formed by curling up the hoop member as shown in FIG. 13(B) by means of spot welding or caulking. As shown in FIG. 13(C), when the outer cylinder is formed while fixing each other end of the wire piece 5 of the pole piece 3 to the hoop member 13 by means of spot welding or caulking, the armature as shown in FIG. 1 is completed. It is noted that the plurality of pole pieces 3 in which the coil 4 is wound around the wire piece 5 are created and the wire piece 5 of the plurality of pole pieces 3 are fixed to the outer peripheral face of the inner cylinder 1 which has been formed by curling up the hoop member in the fourth method. However, it is also possible to create the armature in the state of FIG. 13(B) by fixing the plurality of wire pieces 5 to the hoop member in advance at equal intervals, by creating the inner cylinder 1 by curling up the hoop member on which the wire pieces 5 are fixed and by winding the coil 4 to each wire piece 5 fixed to the inner cylinder 1 at equal intervals. A fifth method for manufacturing the armature will now be explained with reference to process drawings shown in FIG. 14. The fifth manufacturing method is the same with the fourth manufacturing method up to the step of creating the plurality of pole pieces 3 in which the coil 4 is wound around the wire piece 5 (see FIG. 14(A)). One end of the wire piece 5 of each pole piece 3 is jointed to the inner peripheral face of the outer cylinder 2 created by curling up the hoop member so that each pole piece 3 heads the centre by means of spot welding or caulking as shown in FIG. 14(B). When the inner cylinder 1 made of the hoop member is disposed coaxially with the outer cylinder 2 as shown in FIG. 14 (C), the outer peripheral face or the inner cylinder 1 contacts with each other end of the wire piece of the pole piece 3. Then, each other end of each wire piece is jointed with the outer peripheral face by means of spot welding or caulking, thus completing the armature as shown in FIG. 1. FIG. 15 is a sectional view of a high speed spindle motor using a motor armature shown in FIG. 1. a stator 31 which is formed by winding wirings around an iron core, namely, a motor armature is mounted at a position facing the magnet 32 mounted on the inner circumferential surface of the bottomed rotor 33 on the outer circumferential side of the stationary base 34. A central hole 35 is formed at the centre of the stationary base and a lower portion of cylindrical stationary shaft 36 is press-fitted into the central hole 35. As shown in Figs. 15, a flange disc 37 for the bearing is provided coaxially with the stationary shaft 36 in the upper portion of the stationary shaft 36. Although this flange disc 15 is formed integrally with the stationary shaft 36, instead thereof, the flange disc 37 may be formed discretely from the stationary shaft 36 and may be coupled therewith by a suitable means. An oil feed hole 38 for feeding oil is provided in the axial direction of the inner central portion of the stationary shaft 36. An opening of the oil feed hole 38 may be covered by a sealing cover 39 after the replenishment of the oil. An outer circumferential surface of the flange disc 37 is formed as a radial dynamic pressure bearing portion 37f for supporting in the radial direction the rotary member composed of a bottomed rotor 33 and a thrust retaining portion 40. The top surface and the bottom surface of the flange disc 37 are formed into thrust dynamic pressure bearing portions 37a and 37c, respectively, for supporting in the axial direction the rotary member composed of the bottomed rotary 33 and the thrust retaining portion 40. Because the armature of the present invention is structured as described above, assembly is facilitated, the armature can be miniaturised and made more thin and its cost can be reduced. In addition, design changes in size and structure can be flexibly dealt with. Further, the rod (wire piece) and the hoop members used in the manufacturing methods of the inventive armature, facilitate automation and permit changes in design size and structure of the armature swiftly to be dealt with by changing the thickness of the wire piece or the thickness of the hoop member. The aforegoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention.

Claims: A motor armature, comprising: a plurality of pole pieces (3) each comprising a coil (4) wound around a rod (5) formed of a magnetic material; and characterised by further comprising: concentrically disposed first (1) and second (2) cylinders formed of bands of magnetic material, with said plurality of pole pieces extending therebetween and being fixed to both cylinders. A motor armature as claimed in claim 1, wherein said pole pieces are disposed radially at equal intervals. A motor armature according to claim 1 or claim 2, wherein said cylinders are formed by bending a band member of magnetic material. A motor armature according to any one of the preceding claims, wherein each said rod is formed by cutting a wire. A motor armature according to any preceding claim, wherein each said rod is formed of a magnetic core of a material having high saturation magnetic flux density such as low carbon steel or iron, and an outer skin layer of a high magnetic permeability material such as Fe-Co alloy, Fe-Ni alloy or amorphous alloy. A method for manufacturing a motor armature, comprising: a step of creating a plurality of pole pieces (3) in each of which a coil (4) is wound around a rod (5) made of a magnetic material; and characterised by further comprising: a step of fixing one end of each of said plurality of pole pieces to the inner peripheral face of a first cylinder (2) and the other end of each said plurality of pole pieces to the outer peripheral face of a second concentric inner cylinder (1), wherein said cylinders are formed by bending a band member of a magnetic material. A method according to claim 6, wherein said step of fixing comprises: a first step of fixing one end of each of said plurality of pole pieces to the same side of a said band member (1, 2); and a second step of creating either said first cylinder or said second cylinder attached with the pole pieces by bending said band member to which said plurality of pole pieces are fixed so that said plurality of pole pieces are disposed inside or outside of said first cylinder or said second cylinder, respectively. A method according to claim 6 or claim 7, wherein said pole pieces are first disposed outside of said second cylinder, and then forming said first cylinder by bending a band of magnetic material and fixing each other end of said plurality of pole pieces to said first cylinder. A method according to claim 6 or claim 7, wherein said pole pieces are first disposed inside of said first cylinder and then forming said second cylinder from a band of a magnetic material, and fixing each other end of said plurality of pole pieces to said second cylinder. A motor including a motor armature as claimed in any of claims 1 to 6.

Inventors: TAKEHARA ISAMU, TAKEHARA, ISAMU
Applicants: SEIKO SEIKI KK, SEIKO SEIKI KABUSHIKI KAISHA
Application year: 1997
Main classification: H02K15
IPC codes: H02K3, H02K1, H02K15