Abstract: Between a manget (11) on the side of an upper drum (2) and a magnet or electromagnet (12) on the side of a lower drum (3), a force of attraction is exerted. With this force of attraction, pre-load of about 2 Kg is applied to a ball bearing (5) in a direction of an axis, to increase stability of rotation of the upper drum (2). Since the upper drum (2) is borne by the axis (4) with one bearing (5), a center of rotation of the upper drum (2) relative to the axis (4) can be changed by changing a balance among forces of attraction of three magnets or electromagnets (12). With this constitution, a precision rotator which allows correction of the center of rotation can be provided.

Abstract: An axial resonance attenuating apparatus is formed by a disk-shaped attaching member, which is attached to a rotation shaft of a rotation drum apparatus or one of mass objects which are fixed to the both ends of the rotation shaft. A ring-shaped weight is disposed outside the attaching member, and a linking member which is formed by a plurality of straight and flexible support rods partially links the weight and the attaching member. The respective members are formed as one unit by an acrylonitrile-butadiene-styrene copolymer (ABS resin).

Abstract: In a magnetic recording/playback system having a magnetic head drive device for moving a movable head disposed within and mounted to a rotating upper drum in parallel with the axis of the drum, and a fixed drum supporting the upper drum so that the upper drum can rotate, an AC magnetic field generator is disposed along the peripheral surfaces of the drums at a location at which the magnetic tape is not wrapped on the drums. The AC magnetic field generator applies an AC magnetic field to the movable head that varies in the direction of the axis of the drums. Information on the position of the movable head is detected in accordance with the detection signal of the AC magnetic field derived by the movable head and the position of the movable head is controlled by feeding the detected positional infromation back to the magnetic head driving device.