Method of compensating offtrack in disk unit

Abstract

In a disk unit including a plurality of disk media of which any one surface is a servo surface and the other surfaces are all data surfaces; a servo head and data heads arranged on the servo surface and the data surfaces; a positioning mechanism for positioning the servo head and the data heads on desired tracks; and a control unit for controlling the positioning mechanism; the control unit reading servo data from the data surfaces and updates them to find offtrack compensated data, and the head positioning operation being controlled by using the offtrack compensated data and servo information on the servo surface, an offset occurring in the disk unit is compensated by setting the servo track center of the servo head as a reference for positioning the head; writing a pair of servo data for positioning the head onto said data surface while giving a predetermined offset amount which is offset from said track center; giving a predetermined offset amount to thus read and measure the pair of servo data and using the measured value to determine a conversion coefficient; and effecting an offtrack compensation with respect to an offtrack amount detected based on the pair of servo data, by means of a value that is calibrated using the conversion coefficient. By the method, it is possible to accurately effect the offtrack compensation, shorten the time required for measuring the offtrack amount, and improve a reliability of the disk unit.