1. Field of the Invention
The present invention relates to an optical actuator for controlling position of a focusing lens that focuses a laser beam on a disk surface. The optical actuator drives the focusing lens in three directions including focusing, tracking and tilting directions.
2. Description of the Background Art
An Optical actuator drives a focusing lens which forms a beam spot on an information disk, such as a DVD (digital versatile disk) or a CD (compact disk). By driving a focusing lens in a focusing direction, which is orthogonal to the disk surface, and a tracking direction, which is parallel to a radial direction of the disk. The optical actuator controls position of the focusing lens, so that the beam spot is formed on a pit line of the disk accurately. Furthermore, when the disk surface tilts or wobbles with respect to an optical axis of the focusing lens due to disk warpage, the optical actuator performs tilt control by pivotally rotating the focusing lens on an axis along the tangential direction or on an axis-along the radial direction of the disk.
FIG. 10 is a diagram illustrating a conventional optical actuator described in Japanese Patent Laid-Open No. 2001-297460. A focusing lens 101 is fixed to a lens holder 102. Six blade springs 103a–103c, and 103d–103f (103e and 103f are not shown) are fixed to each side of the lens holder 102. Print coils 104a and 104b are fixed to another side of the lens holder 102. A suspension holder 106 and permanent magnets 107a–107d are fixed to a base 105. The print coil 104a is disposed between the permanent magnets 107a and 107b, and the print coil 104b is disposed between the permanent magnets 107c and 107d. The blade springs 103a–103c and 103d–103f are connected to the suspension wires 108a–108c and 108d–108f (108e and 108f are not shown), each of which are fixed to the suspension holder 106.
When a current is supplied to focusing coils built in the print coils 104a and 104b so as to generate electro-magnetic forces in a vertical condition, the lens holder 102 is controlled in the focusing direction Fo. When a current is supplied to tracking coils built in the print coils 104a and 104b so as to generate electro-magnetic forces in the radial direction, the lens holder 102 is controlled in a tracking direction Tk. When a current is supplied to the focusing coils so as to generate electro-magnetic forces having opposite direction in each of the print coils 104a and 104b, rotational moment on an axis in the tracking direction Tk occurs to the lens holder 102. As a result, the lens holder 102 is driven in the tilting direction Ti.
When the lens holder 102 moves in the tilting direction, each of the blade springs 103a and 103c is warped or stretched, and the tilt control becomes unstable. Furthermore, the structure using blade springs requires higher cost and many assembly steps.
It is therefore, a primary object of the invention to provide an optical actuator which is able to perform the tilt control stably and can be produced with low cost.