Patent Publication Number: US-7594239-B2

Title: Magnetic actuator

Description:
BACKGROUND 
   The invention relates to a magnetic actuator, and in particular to a magnetic actuator applied in a reflecting mirror actuator. 
   A magnetic actuator drives electronic components by utilizing a magnet surrounded by coils. The magnet provides magnetic field. When an electric current is occurried in the coil, current flow is perpendicular to magnetic field lines of the magnet. According to Ampere&#39;s Law, relative motion is produced between the coil and the magnet. Resultant motion produced by the magnetic actuator can be applied in optical devices or other conventional mechanism. 
   In  FIG. 1 , a conventional magnetic actuator is shown. The conventional magnetic actuator  1  comprises a hollow cylindrical magnet  10 , a coil  12 , and a yoke base  14 . The magnet  10  can be a permanent magnet with external and internal sides having opposite poles. In this case, the external side has a North pole, and the internal side a South pole. The coil  12  encircles the magnet  10 , for electric current to flow therethrough. The yoke base  14  is connected to a side of the magnet  10 . The magnetic field line  100  produced by the magnet  10  extends radially from an external edge of the magnet  10 , passes through the coil  12 , and enters an internal edge of the magnet  10 , as shown in  FIG. 1 . As a result, if electric current flows through the coil  12 , the electric current is perpendicular to the magnetic field line. Thus, coil  12  will move therefore axially with respect to the magnet  10  as shown by the arrow in  FIG. 1 . The magnetic actuator can be installed in a mechanism that requires relative motion between elements. 
   Another conventional magnetic actuator is shown in  FIG. 2A . The magnetic actuator  2  comprises a solid cylindrical magnet  20 , a yoke  25 , a coil  22 , and a yoke base  24 . The magnet  29  is also a permanent magnet with an upper end, North pole, and a lower end, South pole. The yoke  25  is located above the magnet  20  and connected thereto. The coil  22  encircles the yoke  25 . The yoke base  24  is below the magnet  20 . The magnetic field line  200  produced by the magnet  20  emits axially from the upper end thereof, traveling from the yoke  25  through the coil  22  and entering the magnet  20  from the yoke base  24 . If electric current flows through the coil  22 , current flow is perpendicular to the magnetic field line such that relative axial motion is produced between the coil  22  and the magnet  20 . 
   Another magnetic actuator is shown in  FIG. 2B . The difference from the above mentioned is that a side board  26  is connected to the yoke base  24  located below the magnet  20 . The side board  26  extends from the yoke base  24  to the coil  22  such that the magnetic field line  200  easily extends along the side board  26  and the yoke base  24 , and the magnetic field line  200  passing through the coil  22  can be concentrated, thereby providing improved actuation. 
   However, the actuation of the conventional magnetic actuators is still deficient. For example, in an optical device for transferring light produced from a light source to a light with predetermined intensity and color, the light is projected to produce images. A reflecting mirror actuator is a main component of the optical device to provide high image resolution. The reflecting mirror actuator is commonly provided with a magnetic actuator to direct and project light in different directions, as shown in  FIGS. 3A and 3B . The reflecting mirror actuator  3  comprises a reflecting mirror  31  and a base  32  with a pivot point  33  therebetween. The reflecting mirror  31  can rotate by the pivot point  33  as a center point. A magnetic actuator  30  is disposed at a side of the reflecting mirror  31  and the base  32  to control the movement of the reflecting mirror  31 . When the coil of the magnetic actuator  30  has no current therethrough, as shown in  FIG. 3A , the light is reflected by the reflecting mirror  31  in a predetermined position. When a current is occurred in the coil of the magnetic actuator  30 , as shown in  FIG. 3B , the magnetic actuator  30  actuates the reflecting mirror  31  to rotate by the pivot point  33  such that the light reflected by the reflecting mirror  31  changes to another predetermined position. The reflecting mirror actuator is required to operate rapidly such that the light emitting directions can be changed immediately and resolution increased. Thus, actuation of the conventional actuators is often insufficient because of its structure. In order to satisfy demands for high actuation, the actuator must be enlarged, whereby requirements for more compact design cannot be met. If electric current is increased in the coil, there is also a problem of excessive power consumption. Thus, there is still a need to provide a compact magnetic actuator with high actuation without increasing current of a coil without increased size. 
   SUMMARY 
   Embodiments of the invention provide a magnetic actuator with dense magnetic field lines and high actuation without increased size or current. 
   Further provided is a magnetic actuator applicable in a reflecting mirror actuator of an optical device, increasing actuation thereof. 
   The magnetic actuator comprises two magnets arranged axially with co-repulsion with a yoke disposed therebetween. The coil surrounds and is positioned corresponding to the yoke. Magnetic field lines produced by the magnets extend from the yoke, pass through the coil, and enter the other ends of the magnets. The distance between magnets is appropriately reduced such that density of the magnetic field lines is increased, thereby increasing magnetic force of the coil. 
   Accordingly, a gap between the magnets is less than twice the thickness of any magnet. 
   The disclosed structure of the magnet actuator can be arranged differently or overlap. Two yokes can be disposed respectively between two sets of two magnets arranged axially with repulsion therebetween. Each set comprises a coil, surrounding each yoke. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein: 
       FIG. 1  is a schematic top and side cross section of a conventional magnetic actuator; 
       FIG. 2A  is a schematic top and side cross section of another conventional magnetic actuator; 
       FIG. 2B  is a schematic top and side cross section of yet another conventional magnetic actuator; 
       FIG. 3A  is a schematic view of a magnetic actuator applied in a stationary reflecting mirror actuator if the magnetic actuator have not been actuated; 
       FIG. 3B  is a schematic view of a magnetic actuator applied in a stationary reflecting mirror actuator if the magnetic actuator have been actuated; 
       FIG. 4A  is a schematic top and side cross section of a magnetic actuator according to a first embodiment of the invention; 
       FIG. 4B  is a schematic top and side cross section of a magnetic actuator according to a second embodiment of the invention; 
       FIG. 4C  is a schematic top and side cross section of a magnetic actuator according to a third embodiment of the invention; 
       FIG. 4D  is a schematic top and side cross section of a magnetic actuator according to a fourth embodiment of the invention; 
       FIG. 5  is a schematic top and side cross section of a magnetic actuator according to a fifth embodiment of the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 4A  is a schematic top and side cross section of a magnetic actuator according to a first embodiment of the invention. The magnetic actuator  4  comprises a first magnet  40 , a second magnet  40 ′, a coil  42 , and a yoke  43 . The first magnet  40  and the second magnet  40 ′ are axially arranged with repulsion therebetween. In this embodiment, the North pole of the first magnet  40  faces to the North pole of the second magnet  40 ′, generating repulsion therebetween. The yoke  43  is disposed between the first magnet  40  and the second magnet  40 ′. The coil  42  surrounds and is positioned corresponding to the yoke  43 . Since the North poles of two magnets  40 ,  40 ′ are arranged axially and face to each other, magnetic field line  400  produced from the center of the yoke  43  extends radially out of and around the coil  42 , and enters the lower edge (South pole) of first magnet  40  and the upper edge (South pole) of second magnet  40 ′, respectively. Thus, when current flows is occurred through the coil  42 , current flows and magnetic field lines are also perpendicular to each other such that the magnetic force will be produced to move the coil  42  axially with respect to the first magnet  40  and the second magnet  40 ′ therefore. 
   According to the disclosed structure, thicknesses of the first and second magnets  40 ,  40 ′ are substantially the same. Moreover, the gap therebetween can be less than twice the thickness of the first or second magnet  40 ,  40 ′. The reduced gap results in magnetic field lines  400  produced by the first or second magnet  40 ,  40 ′ being densely formed, extending radially from the yoke  43 . As a result, the density of the magnetic field lines  400  is increased. Provided with the same current flow and power supply to the coil  42  without increasing the size of the actuator, the magnetic actuator  4  of the invention provides improved actuation. 
   The magnetic actuator  4  can be applied in a reflecting mirror actuator of an optical device. Thanks to the above mentioned structure, the size of the magnetic actuator  4  and current flow of the coil can be maintained, to provide improved actuation. Thus, the magnetic actuator  4  satisfies requirements of the reflecting mirror actuator to successfully actuate the reflecting mirror rotating about a pivot point and providing rapid light interchange for higher resolution. The first magnet  40  and first coil  42  of the magnetic actuator  4  can be connected to a base of the reflecting mirror actuator or the mirror. Thus, relative motion is produced between the first and second magnets  40  and  42  for actuating the reflecting mirror rotating about the pivot point. 
     FIG. 4B  is a schematic top and side cross section of a magnetic actuator according to a second embodiment of the invention. Another magnetic actuator  4  comprises a first magnet  40 , a second magnet  40 ′, a coil  42 , and a yoke  43 , as well as a yoke base  44  connected to a lower edge of the first magnet  40 . The yoke base  44  can be permeable such that the density of the magnetic field lines  400  near the coil  42  and the lower edge of the first magnet  40  is increased, providing improved actuation. The yoke base  44  can be rectangular or circular. 
     FIG. 4C  is a schematic top and side cross section of a magnetic actuator according to a third embodiment of the invention. The magnetic actuator  4  comprises a first magnet  40 , a second magnet  40 ′, a coil  42 , a yoke  43 , and a yoke base  44 . The difference is that the yoke base  44  further comprises a side board  46  near the first magnet  40 . The side board  46  extends axially from the yoke base  44  to the coil  42 . In a preferred embodiment, the side board  46  can encircle the first magnet  40  entirely. The side board  46  is of the same permeable material as the yoke base  44 . Thus, the magnetic field lines  400  passing through the coil  42  can effectively extend along the side board  46  and the yoke base  44 , and return to the lower edge of the first magnet  40 . Thus, density of the magnetic field lines  400  is increased, providing improved actuation. 
     FIG. 4D  is a schematic top and side cross section of a magnetic actuator according to a fourth embodiment of the invention. The magnetic actuator  4  comprises a first magnet  40 , a second magnet  40 ′, a coil  42 , and a yoke  43 . A central shaft  48  connected to the coil  42  penetrates the first magnet  40 , the second magnet  40 ′, and the yoke  43 . When the magnetic actuator  4  is actuated, a relative axial motion is produced between the central shaft  48  and the coil  42  with respect to the first magnet  40 , the second magnet  40 ′, and the yoke  43 . In practice, the central shaft  48  and the coil  42  or the first magnet  40 , the second magnet  40 ′, and the yoke  43  can be optionally fixed together. 
     FIG. 5  is a schematic top and side cross section of a magnetic actuator according to a fifth embodiment of the invention. The magnetic actuator  5  comprises a first magnet  50 , a second magnet  50 ′, a third magnet  50 ″, a first coil  52 , a second coil  52 ′, a first yoke  53 , and a second yoke  53 ″. The first magnet  50  and the second magnet  50 ′ are axially arranged with repulsion therebetween. The second magnet  50 ′ and the third magnet  50 ″ are also axially arranged with repulsion therebetween. In this embodiment, the first magnet  50  has its North pole facing to the North pole of the second magnet  50 ′. At a meanwhile, the second magnet  50 ′ has its South pole facing to the South pole of the third magnet  50 ″. The first yoke  53  is disposed between the first magnet  50  and the second magnet  50 ′. The second yoke  53 , is disposed between the second magnet  50 ′ and the third magnet  50 ″. The first coil  52  surrounds and positioned corresponding to the first yoke  53 . The second coil  52 ′ surrounds and positioned corresponding to the second yoke  53 ′. Thus, according to the disclosed arrangement, North poles of the first and second magnets  50 ,  50 ′ face to each other such that the magnetic field lines  400  produced therefrom extend from a center of the first yoke  53 , pass through the coil  52 , and enter a lower edge (South pole) of the first magnet  50  and an upper edge (South pole) of the second magnet  50 ′. Meanwhile, South poles of the second and third magnets  50 ′,  50 ″ face each other such that the magnetic field lines  400  emit from a lower edge (North pole) of the second magnet  50 ′ and an upper edge (North pole) of the third magnet, radially pass through the second coil  52 ′, and enter the upper edge (South pole) of the second magnet  50 ′ and the lower edge (South pole) of the third magnet  50 ″. Thus, current through the first coil  52  is perpendicular to the magnetic field lines such that the first magnetic force will be produced to move the first coil  52  axially with respect to the first and second magnets  50 ,  50 ′. Moreover, the first magnetic force will be also produced to move the second coil  52 ′ axially with respect to the second and third magnets  50 ′,  50 ″. 
   As shown in  FIG. 5 , current flows from the left portion of the first coil  52  in an outward direction perpendicular to paper surface and from the right portion of the first coil  52  into the paper surface. According to the Ampere&#39;s Law, current direction of the first coil  52  depends on direction of the magnetic field lines of the first and second magnets  50 ,  50 ′, and thus, the first coil  52  can move downward axially. Similarly, if current flows out of the paper surface from the right portion of the second coil  52 ′ and perpendicularly therein from the left portion thereof. According to the Ampere&#39;s Law, current direction of the second coil  52 ′ depends on direction of the magnetic field lines of the second magnet  50 ′ and the third magnet  50 ″, and thus, the second coil  52 ′ can move downward axially. If the first coil  52  connects to the second coil  52 ′, actuation is doubled. Hence, according to the structure disclosed in the first embodiment, the structure can overlap or be combined to produce multiple actuations to fulfill various requirements of driving elements. 
   While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.