Lens driving device comprising magnetic circuit with high magnetic efficiency
A lens driving device includes a lens holder including a tubular portion for holding a lens assembly, a driving coil fixed to the lens holder so as to position around the tubular portion, and a yoke including a permanent magnet opposite to the driving coil. The yoke includes an outer hollow cylindrical portion having a rectangular cylindrical shape, the permanent magnet includes at least four permanent magnet pieces each having a rectangular cross section. Four magnetic circuit auxiliary members are disposed between four corners of the outer hollow cylindrical portion of the yoke and four ones of the permanent magnet pieces that are disposed at the four corners of the outer hollow cylindrical portion of the yoke.
1. A lens driving device comprising:
a lens holder including a tubular portion for holding a lens assembly;
a driving coil fixed to said lens holder so as to be positioned around the tubular portion;
a yoke comprising a permanent magnet disposed opposite to said driving coil; and
upper and lower leaf springs disposed respectively on upper and lower sides of the tubular portion of said lens holder in a direction of an optical axis, said upper and lower leaf springs supporting said lens holder in the direction of the optical axis shiftably so as to position said lens holder in a radial direction,
wherein each of said upper and lower leaf springs comprises an inner end portion mounted to said lens holder and an outer end portion mounted to said yoke, whereby said lens holder is positionally adjustable in the direction of the optical axis, by energizing said driving coil, according to interaction between a magnetic field of said permanent magnet and a magnetic field due to a current flowing through said driving coil,
wherein said yoke includes an outer hollow cylindrical portion having a rectangular cylindrical shape,
wherein said permanent magnet comprises at least four permanent magnet pieces each having a rectangular cross section,
wherein said lens driving device further comprises four magnetic circuit auxiliary members each of which is made of a ferromagnetic material and which are disposed between four corners of said outer hollow cylindrical portion of said yoke and four of said permanent magnet pieces that are disposed at the four corners of said outer hollow cylindrical portion of said yoke.
2. The lens driving device as claimed in claim 1 , wherein each of said four magnetic circuit auxiliary members has a triangular shape in cross section in a plane orthogonal to the direction of the optical axis.
3. The lens driving device as claimed in claim 1 , wherein each of said four magnetic circuit auxiliary members is made of a pressed metal.