JPS6462835A - Lens focusing actuator - Google Patents

Abstract

PURPOSE:To constitute all the parts of a moving section of ring-shaped parts so that the size and weight of the moving section are reduced by forming all the parts of the moving section into the ring shape and using a permanent magnet consisting of an Nd-Fe-B rare earth in the moving section. CONSTITUTION:All the parts of the moving section having the construction in which the permanent magnet 105 is used in the moving section as a means for driving an objective lens 101 of an optical head are constituted of the ring-shaped parts. The cylindrical permanent magnet 105 which is formed by melting an alloy having the basic compsn. consisting of neodymium (Nd), iron (Fe) and boron (B) to a mixed state of crystal and amorphous by using a melt spinning method, grinding the melt and putting the resultant magnetic into a mold, then subjecting the powder to a hot compaction treatment and is further pressurized in the longitudinal direction of the cylinder and is thereby magnetized in the same direction is provided as the permanent magnet 105 of the moving section. Auxiliary magnetic poles 103, 104 are bonded to both ends thereof. The auxiliary magnetic poles 103, 104 are formed by mixing Fe, Co and Mn, adding zinc stearate to the mixture at the same ratio as the ratio of Mn, molding the mixture and dewaxing the molding in a vacuum, then sintering the molding in an Ar atmosphere. Since the auxiliary magnetic poles have the larger saturation magnetic flux density than the saturation magnetic flux density of pure iron, etc., these magnetic poles contribute to the reduction in the size and weight of the moving section as compared to the case of using other soft magnetic materials. High speed responsiveness is thus obtd.