Abstract: A disk cartridge which contains an optical disk, comprising a first half shell, and a second half shell which is openable against the first half shell, wherein the first half shell is formed with notches to expose a part of the circumference of the optical disk.

Abstract: A viscoelastic substance which is useful in an objective lens driving apparatus has magnetic particles dispersed therein for generating a force for restoring deformation of the viscoelastic substance when an external force acts upon the viscoelastic substance in the presence of an external magnetic field.

Abstract: An objective lens driving apparatus includes an objective lens held by a movable member. The movable member is supported on a base by a support mechanism to be movable in a predetermined direction. Magnetic field forming unit is fixed to the base so as to apply a magnetic field to the movable member. Focusing coils and tracking coils are fixed to the movable member to drive the movable member in the predetermined direction in cooperation with the magnetic field. Viscoelastic substances for absorbing vibration of the movable member are arranged between the focusing coils and the magnetic unit and between the tracking coils and the unit. The viscoelastic substance has a viscoelastic material and magnetic material dispersed therein.

Abstract: An objective lens driving apparatus is provided which can restrain hysteresis phenomena in the relationship between semi-static displacements and forces in a focusing direction of the objective lens. The apparatus can also maintain the balance of force even when the objective lens is shifted in a focusing or tracking direction. Thus, the objective lens can be readily prevented from tilting. The apparatus also has a simplified configuration that can readily start up control operations in servomechanism. Thus, stable control characteristics of the apparatus can be achieved.