Position sensing system for disc drive magnetic microactuators

A method for sensing the precise position of a read/write head in an apparatus having a primary actuator for coarse positioning of the head and a magnetic microactuator for fine positioning of the head, wherein the microactuator includes a voice coil motor (VCM) with a VCM coil, the method comprising steps of:

• a) providing a fixed member attached to the primary actuator and a moveable member attached to the fixed member whereby the moveable member may move in relation to the fixed member in response to current through the VCM coil fastened to the moveable member;
• b) applying a high frequency signal to the VCM coil via a pair of terminals at opposite ends of the VCM coil;
• c) positioning a first sense coil on the fixed member near the VCM coil such that the first sense coil can receive a portion of the high frequency signal transmitted by the VCM coil by mutual magnetic coupling;
• and
• d) measuring the portion of the high frequency signal coupled into the first sense coil.

A position sensing system in a head disc assembly of a disc drive comprising:

• a primary actuator coupled to a microactuator supporting a transducer;
• and
• means for sensing a movement of the microactuator relative to the primary actuator;
• a fixed member attached to the primary actuator;
• a moveable member attached to the fixed member by an attachment device which permits the moveable member to move in relation to the fixed member along a predetermined pathway, wherein a voice coil motor coil of the microactuator is attached to the moveable member;
• a pair of terminals at opposite ends of the voice coil motor coil for receiving a high frequency signal applied to the voice coil motor coil;
• and
• a sense coil attached to the fixed member and positioned near enough to the voice coil motor coil to receive a measurable portion of the high frequency signal transmitted from the voice coil motor coil through mutual magnetic coupling.