This application claims priority under 35 U.S.C. ยง119 to Japanese Patent application No. JP2008-243243 filed on Sep. 22, 2008, the entire contents of which are hereby incorporated by reference.
The present invention relates to an electric motor apparatus for use, for example, in small electronic devices such as mobile phones and digital cameras.
There are small electronic devices, such as mobile phones, having a camera function, for example. Such small electronic devices use an electric motor apparatus having an electric motor to drive a lens system.
Japanese Patent Application Publication No. 2004-364490 discloses such an electric motor apparatus suitable for use in small electronic devices or the like. The electric motor of this apparatus, however, has a structure comprising a rotor having a permanent magnet with two magnetic poles and an electromagnet with two magnetic poles disposed around the rotor. This motor structure has likelihood that the rotor may fail to rotate in a predetermined direction when started, or that even if the rotor rotates in a predetermined direction, the rotor may start to rotate in a reversed direction when an impact is applied to the apparatus.
Japanese Patent No. 279,666 also discloses an electric motor apparatus suitable for use in small electronic devices or the like. The electric motor of this apparatus has a structure comprising a rotor having a permanent magnet with four magnetic poles and an electromagnet with two magnetic poles disposed around the rotor. This electric motor apparatus can fix the rotational direction of the rotor. However, because the rotor needs four magnetic poles to be magnetized, the magnetic efficiency is degraded, and hence large output torque cannot be obtained.
The present invention has been made in view of the above-described circumstances. Accordingly, an object of the present invention is to provide an electric motor apparatus using a rotor having a permanent magnet with two magnetic poles and yet capable of controlling the rotational direction of the rotor to a desired direction.
The present invention provides an electric motor apparatus including a rotor having a rotation axis, a permanent magnet having two magnetic poles spaced from each other by approximately 180 degrees about the rotation axis, and a stator having first to third magnetic pole portions successively disposed around the rotor, the first to third magnetic pole portions being spaced from each other in a circumferential direction about the rotation axis, and respectively having magnetic pole surfaces disposed to face the rotor. The stator further has connecting portions each connecting between an associated pair of adjacent ones of the first to third magnetic pole portions around the rotor. The second magnetic pole portion extends radially outward with respect to the rotation axis from the magnetic pole surface of the second magnetic pole portion. The first and third magnetic pole portions extend radially outward with respect to the rotation axis and away from each other from their respective magnetic pole surfaces. The connecting portions each have a reduced cross-sectional area that is gradually reduced from the associated pair of adjacent magnetic pole portions toward a substantially central region between the associated pair of adjacent magnetic pole portions and each have a smallest cross-sectional area at the substantially central region between the associated pair of adjacent magnetic pole portions. The electric motor apparatus further includes a first electromagnetic coil and a second electromagnetic coil. The first electromagnetic coil induces a magnetic circuit that passes through the first and second magnetic pole portions. The second electromagnetic coil induces a magnetic circuit that passes through the second and third magnetic pole portions. The first and second electromagnetic coils are set parallel to and at opposite sides of the second magnetic pole portion. The first electromagnetic coil has one end magnetically coupled to the first magnetic pole portion, and an other end magnetically coupled to the second magnetic pole portion. The second electromagnetic coil has one end magnetically coupled to the third magnetic pole portion, and an other end magnetically coupled to the second magnetic pole portion. The first and second electromagnetic coils are selectively excited to control the rotation of the rotor.
In this electric motor apparatus, the rotor has two magnetic poles. Thus, it is possible to obtain increased output torque as compared to an electric motor apparatus whose rotor has four magnetic poles as disclosed in the aforementioned Japanese Patent No. 279,666. Meanwhile, the stator has three magnetic poles. Therefore, the rotor can be rotated in a desired direction by controlling the application of an electric current to the electromagnetic coils. In addition, since the connecting portions between the first to third magnetic pole portions are shaped narrow in their middle regions, and the magnetic reluctance of the connecting portions is increased, and thus, the mutually adjacent magnetic pole portions are magnetically isolated from each other.
The electric motor apparatus may be arranged as follows. The stator has a pass-through hole for coaxially accommodating the rotor, and the pass-through hole is defined by the magnetic pole surfaces of the first to third magnetic pole portions and respective inner surfaces of the connecting portions. The connecting portions extending between the first and second pole portions and between the second and third magnetic pole portions, and the stator has notches formed at the pass-through hole, at positions adjacent to the magnetic pole surfaces of the first and third magnetic pole portions. The notches extend substantially parallel to the rotation axis. With this structure, when the electromagnetic coils are deenergized, the rotor can be held in a stable position since the magnetic flux from the permanent magnet of the rotor passes more through the magnetic pole surface that one of the magnetic poles of the rotor faces adjacently.
The electric motor apparatus may further include a notch that extends substantially parallel to the rotation axis and is formed in the magnetic pole surface of the second magnetic pole portion. That is, the magnetic pole surface of the second magnetic pole portion is divided in the circumferential direction into two areas at the left and right sides of the notch. With this structure, when the rotor is stopped, one of the two magnetic poles of the rotor adjacently faces the left or right portion of the magnetic pole surface of the second magnetic pole portion, and when the electromagnetic coils are deenergized, the magnetic flux from the permanent magnet of the rotor passes more through the portion of the magnetic pole surface that the magnetic pole adjacently faces. Thus, the rotor can be held stably when the electromagnetic coils are deenergized.
Further, the electric motor apparatus may further include two notches that extend parallel to the rotation axis and may be formed at spaced positions in the magnetic pole surface of the second magnetic pole portion, the two notches spaced from each other with a substantially central region of the magnetic pole surface being interposed between the two notches.
The electric motor apparatus may be arranged as follows. The stator is a member that is thin and flat in the direction of the rotation axis, and the apparatus further includes a thin and flat first and second frame member that hold the stator between the frames from both sides in the direction of the rotation axis. The first frame member has a pass-through hole aligned with the pass-through hole of the stator in the direction of the rotation axis and a rotor support member fitted in the pass-through hole. The rotor is rotatably supported by the rotor support member.
By providing the rotor support member as a distinct member separated from the frame member, the rotor support member can be formed by precision molding. Thus, the rotor can be positioned accurately.
The stator and the permanent magnet of the rotor may be formed to have substantially the same thickness in the direction of the rotation axis. The purpose of this is to improve the magnetic efficiency between the stator and the rotor.
The electric motor apparatus may further include a speed reduction gear that outputs the rotation of the rotor to the outside of the electric motor apparatus after reducing the speed of the rotation. The speed reduction gear may have an output gear shaft and an intermediate gear shaft that transmits the rotation of the rotor to the output gear shaft. The second magnetic pole portion may have pass-through holes through which the output gear shaft and the intermediate gear shaft are inserted, respectively. The purpose of this arrangement is to install the speed reduction gear intensively at the second magnetic pole portion and to thereby reduce the overall size of the apparatus.
The arrangement may be as follows. The stator has extensions that extend in mutually opposite lateral directions from an extended end portion that is extended radially outwardly from the magnetic pole surface of the second magnetic pole portion. Thus, the stator has a substantially H-shape as a whole. The first and second electromagnetic coils each comprising a flat plate-shaped magnetic member and a coil wire wound around the magnetic member, the flat plate-shaped magnetic members of the first and second electromagnetic coils having one end portions engaged and connected to the first and third magnetic pole portions, respectively, and other end portions engaged and connected to the corresponding extensions of the third magnetic pole portion, respectively.
With the above-described shape of the stator and the configuration of the electromagnetic coils, the electric motor apparatus can be reduced in size.
The arrangement may also be as follows. The stator has extensions extending in mutually opposite lateral directions from an extended end portion of the second magnetic pole portion, the extended end portion that is extended radially outwardly from the magnetic pole surface. Thus, the stator has a substantially H-shape as a whole. The first and second electromagnetic coils each comprise a flat plate-shaped magnetic member and a coil wire wound around the magnetic member. The magnetic members of the first and second electromagnetic coils have one-end portions that are engaged and connected to the first and third magnetic pole portions, respectively, and other end portions are connected to respective end portions of the corresponding extensions of the third magnetic pole portion. The first and second frame members are stacked to hold the stator and the first and second electromagnetic coils between the frame members from both sides in the direction of the rotation axis. The stacked first and second frame members, the stator and the magnetic members of the first and second electromagnetic coils have pass-through holes in their portions superimposed in the direction of the rotation axis, the pass-through holes being aligned with each other in the direction of the rotation axis. Fastening screws are passed through the pass-through holes to secure the first and second frame members, the stator and the first and second electromagnetic coils to each other.
The present invention will be explained below by way of embodiments shown in the accompanying drawings.
The rotor 135 is in the shape of a thin disk and made of a permanent magnet having two magnetic poles N and S magnetized at respective positions spaced from each other by approximately 180 degrees about its center axis, i.e. rotation axis.
The stator 120 has a pass-through hole 119 that accommodates the rotor 135. The stator 120 has a first magnetic pole portion 112, a second magnetic pole portion 114 and a third magnetic pole portion 116 circumferentially spaced from each other around the pass-through hole 119 and further has connecting portions 122, 124 and 126 that connect between the mutually adjacent magnetic pole portions, respectively. The radially inner surfaces of the first, second and third magnetic pole portions 112, 114 and 116 define magnetic pole surfaces 112a, 114a and 116a, respectively, and the magnetic pole surfaces constitute the wall surface of the pass-through hole 119 in cooperation with the inner surfaces of the connecting portions 122, 124 and 126. The second magnetic pole portion 114 extends radially outward with respect to the rotation axis. The first and third magnetic pole portions 112 and 116 extend radially outward with respect to the rotation axis and away from each other. The connecting portions 122, 124 and 126 each have a reduced cross-sectional area that is gradually reduced from an associated pair of magnetic pole portions that are mutually adjacent to each other toward a substantially central region between the associated pair of the magnetic pole portions and each have the smallest cross-sectional area at the substantially central region between the associated pair of adjacent magnetic pole portions. The first to third magnetic pole portions 112, 114 and 116 assume, in combination, a substantially T-shape (substantially Y-shape). In the illustrated example, however, the second magnetic pole portion 114 has extensions 114b and 114c extending in mutually opposite lateral directions from the extended end portion of the second magnetic pole portion, the end portion remote from the rotor 135. Thus, the stator 120 has a substantially H-shape as a whole.
The first electromagnetic coil 140 and the second electromagnetic coil 142 are formed by winding a copper wire around thin plate-shaped magnetic members 140a and 142a made, for example, of a high-permeability alloy of iron and nickel. The first and second electromagnetic coils 140 and 142 are disposed parallel to and at the opposite sides of the second magnetic pole portion 114. The opposite ends of the magnetic member 140a of the first electromagnetic coil 140 are connected to the first magnetic pole portion 112 and the extension 114b (of the second magnetic pole portion 114) by fastening screws 170 through the respective pass-through holes 125. The opposite ends of the magnetic member 142a of the second electromagnetic coil 142 are engaged and connected to the third magnetic pole portion 116 and the extension 114c (of the second magnetic pole portion 114) by fastening screws 170 through the respective pass-through holes 125. When the first electromagnetic coil 140 is excited, the resulting electromagnetic flux passes through a magnetic circuit formed by the first magnetic pole portion 112, the rotor 135, the second magnetic pole portion 114 and the first electromagnetic coil 140. Whether the electromagnetic flux passes through the magnetic circuit clockwise or counterclockwise is determined by the direction of current application to the electromagnetic coil, as will be described later by using
Because the connecting portions 122, 124 and 126 are shaped narrow in their middle regions as stated above, the magnetic reluctances between the magnetic pole surfaces 112a, 114a and 116a increase. Consequently, the magnetic flux concentrates on each of the magnetic pole surfaces 112a, 114a and 116a, the magnetic interaction between the magnetic pole surfaces 112a, 114a and 116a and the magnetic poles of the rotor 135 is intensified, and thus, the torque applied to the rotor 135 is increased. It should be noted that the electromagnetic flux should be substantially prevented from passing through the connecting portions 122, 124 and 126. For this purpose, a low-permeability material such as stainless steel may be welded to portions between the magnetic pole portions to form the connecting portions 122, 124 and 126. It is also possible to provide a space between each pair of adjacent magnetic pole portions. As shown in part (a) of
Part (b) of
Part (c) of
In the electric motor apparatus 100 according to the present invention, necessary magnetic poles are induced in the three magnetic pole portions 112, 114 and 116 around the rotor 135 by properly controlling the supply (application) of an electric current to the electromagnetic coils 140 and 142, and thus, the rotor 135, which comprises a permanent magnet with two magnetic poles, rotates in a desired direction.
Although some embodiments of the present invention have been described above, the present invention is not limited to the foregoing embodiments. The electric motor apparatus of the present invention can be used for performing various drive operations, e.g., for driving the diaphragm or spherical aberration correcting unit of a camera, in addition to the illustrated application examples. The electric motor apparatus of the present invention can incorporate a drive IC (drive integrated circuit; not shown), and thus can be used for a wide range of applications.
Number | Date | Country | Kind |
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2008-243243 | Sep 2008 | JP | national |