A near zero skew actuation mechanism for hard disk drives

The rotation of the voice coil motor (VCM) actuator in a hard disk drive results in a skewed actuation. The difference in skew angles, between the inner diameter (ID) and the outer diameter (OD) can be as large as 25°–35° in conventional 3.5″ and 2.5″ hard disk drives. A large skew angle causes an increase in side reading and writing, and thus reduces the achievable recording density. A large skewed actuation also degrades the head flying performance and complicates the servo loop. In this paper, a four link actuation mechanism which can be designed to achieve near zero skew actuation in hard disk drives is presented. The profiles of the arm, suspension, and links are optimized such that the skew angle is close to zero when the VCM actuator rotates from the ID to the OD. Finite element analysis is employed to study the resonance frequencies, frequency responses and shock performance of the mechanism. The study shows that the four link mechanism does not degrade the resonance performance along the tracking direction and the shock performance compared to a conventional actuator. Experimental motion analysis shows that actuation response speed of the mechanism is 50 % slower than that of a conventional actuator. The recording density gain due to a substantial zero skew actuation is 12–18 % compared to conventional actuations.