| 摘要 |
<p>Data storage apparatus of the type employing a stack of rotatable storage disks accessible by a plurality of data heads ganged for movement over the data surfaces. The position of a data head during track following operations over a selected data surface being controlled by a hybrid servo signal consisting of low frequency components of position information signals derived from servo sectors around the data track being followed added to which are high frequency components of continuous position information signals derived either from a dedicated servo surface forming part of the stack or from an external position transducer. The continuous position information being provided by a servo transducer, which is also ganged to the data heads, in the form of two cyclic quadrature signals (90.degree. out of phase with each other) each having portions which are linear and co-extensive over the whole range of head displacement. The apparatus including servo control circuits for detecting during data track following position (caused for example by temperature variations or mechanical vibrations) beyond the linear region of the corresponding one of the two quadrature signals supplying the high frequency components and, upon such detection, switching to an adjacent linear portion of the other signal, or the inverse of the other signal, to either of which has been added an appropriate d.c. offset so that the linear portion of this other signal becomes an effective extension of the linear portion of the continuous servo signal corresponding to the data track being followed. By this means the a.c. gain of the servo circuits is maintained constant thereby improving the servo loop performance.</p> |
