Magnetic head and disk tester with pitch correction

Abstract

A magnetic head and disk tester provides accurate positioning of a magnetic read-write head over a magnetic disk by means of a coarse positioning mechanism and a fine positioning mechanism. The coarse positioning mechanism includes a stepper motor, a lead screw, a nut, rear sliders and a housing. The fine positioning mechanism includes a piezoelectric actuator, slides and a carriage. The positioning displacements are along a linear axis, which lies on a horizontal plane. The carriage is connected to the housing via the fine positioning mechanism, which then moves the carriage with respect to the housing. Two pairs of linear encoders are mounted on the carriage about the axis and measure the position of the magnetic read-write head with respect to the magnetic disk. Each pair is mounted such that the pairs lie in separate horizontal planes. One linear encoder on each pair is mounted to the right of the magnetic read-write head and the other to the left of it, the magnetic read-write head being equal distances from the two linear encoders of each pair. The magnetic read-write head is mounted on the carriage with an offset from each pair of linear encoders in the vertical direction. Pitch during the fine positioning movement causes the head to move a different amount than that measured by any one of the pairs of linear encoders. By using both pairs of encoders, the amount of pitch is determined. A feedback circuit responsive to that determination causes the fine positioned to move the head to the correct pitch.