Correction-lens-moving voice coil motor, anti-vibration device, interchangeable lens unit and optical apparatus
A voice coil motor for moving a correction lens including a magnet unit having a pair of yokes and at least one permanent magnet for defining a magnetic gap, and a coil disposed in the magnetic gap. The permanent magnet having different magnetic poles adjacent to each other along the movement direction on a surface opposing the magnetic gap; the width of the permanent magnet in the movement direction being two times the width Wm of the magnetic poles; the width Wa of the coil in the movement direction being smaller than the width 2Wm of the permanent magnet; and the effective conductor width Wb of the coil, the magnetic pole width Wm of the permanent magnet and the longest movement distance St of the correction lens meeting the conditions of Wm=(Wb+St)×K, wherein K is a constant meeting 1<K≦1.5.
1. An anti-vibration device comprising a correction lens, a frame supporting said correction lens and arranged in a holding member such that it can move in two directions perpendicular to the optical axis, and a pair of voice coil motors arranged in said holding member such that said frame can linearly move in said two directions;
each voice coil motor comprising a magnet unit comprising a pair of yokes fixed to said holding member for providing a magnetic gap and a pair of permanent magnets fixed to a surface of each yoke opposing the magnetic gap, and a flat coreless coil disposed in said magnetic gap and fixed to said frame;
each permanent magnet having different magnetic poles adjacent to each other along the movement direction of said coil on a surface opposing the magnetic gap;
both permanent magnets having different magnetic poles opposing via said magnetic gap;
wherein the flat coreless coil has an elongated circular shape comprising multi-layer winding having two linear portions parallel to each other and two semicircular portions connecting ends of the linear portions, and a coreless portion, and moves linearly in a direction perpendicular to the linear portions in a plane of the flat coreless coil;
when a width of said permanent magnets in a movement direction is two times a width Wm of said magnetic poles, a width Wa of said flat coreless coil in the movement direction being smaller than the width 2Wm of said permanent magnets; and an effective conductor width Wb of said flat coreless coil, the magnetic pole width Wm of said permanent magnets and the longest movement distance St of said correction lens meeting the conditions of Wm=(Wb+St)×K, wherein K is a constant meeting 1<K≦1.5;
the longest movement distance St of said correction lens being in a range of 1-4 mm; and
a peak value of a magnetic flux density distribution in said magnetic gap being 0.5 T or more;
whereby said correction lens is moved by said flat coreless coil to which current is supplied, to carry out the correction of hand movement.
2. An interchangeable lens unit comprising the anti-vibration device recited in claim 1 , an imaging lens and a focus lens in a barrel.
3. An optical apparatus which comprises the anti-vibration device recited in claim 1 , and forms an optical image on an image sensor through an optical system comprising an imaging lens, a focus lens and the correction lens.