Design of flexural pivot for use in hard disc drive actuator

Abstract

A cross leaf flexural pivot is proposed and designed for use in disc drive actuator to replace the currently used ball bearing system. The static and dynamic performances of the proposed design are investigated using finite element analysis. It is shown that flexural pivot can achieve a translatory stiffness comparable to currently used ball bearing. The tilt stiffness is lower than that of ball bearing. The design is prototyped and the life cycling test shows that the prototype can work for more than 3 million life cycles without any failure. Our experimental results show that the single-stage servo loop using the flexural pivot can achieve the performances of open-loop bandwidth of 630 Hz and closed loop bandwidth of 1100 Hz, with phase margin of 60°and gain margin of 6.6 dB. When attaching an actuated suspension to from a dual stage servo loop, we show that the performances as open-loop bandwidth of 1700 Hz with the phase margin of 45°and gain margin of 7 dB. IntroductionTo stay competitive in the highly volatile HDD industry, cost cutting is an attractive and viable option. Currently ball bearings are used in hard disc drives to provide rotational mechanism. Ball bearings operate with friction and damping, causing non-linearity in the actuator and therefore make the position control more difficult, Prater (1995) and Liu et al. (2000). Flexure bearings, on the other hand, are simpler in structure and therefore is potential for low cost compare with the current ball bearing systems. The objective of the research involved in this paper is thus to design a flexural pivot, which can replace the bearing currently used in hard disc drives without sacrificing the performance.Previously an actuator comprised of parallel pair of steel leaf springs which support a moving coil in a voice coil motor (VCM) was proposed by IBM Research Division, Chainer et al. (1989 and Sri-Jayantha et al. (1991). In the design, the actuator translation is produced by the bending of the flexible ends. The motion generated without any metal contact typical of conventional ball bearing based actuator systems used in disc files. Therefore, the system does not generate any particulate debris or require any lubrication, resulting in very clean operation. The absence of metal contact eliminates stictional forces, offering potential for very fine motion control. In addition, the translatory motion of the actuator produces a small ±1.0°skew angle at the recording head, much lower than conventional rotary designs. The investigation also indicates that the presence of the significant bias forces and low-frequency modes are clearly inevitable in a flexural actuator. In the work reported by He et al. (2002), the disk drive actuator can be designed with a slant suspension, which achieves ±2.0°skew angle. The dynamic performance of the slanted actuator does not change significantly to the actuator assembly without slanting the suspension. However, as the design of the small skew actuator needs to increase the actuator arm length, this will cause the reso...

Rotational elastic micro joint based on helix-augmented cross-spring design for large angular movement

“…Cross-springs are widely used to achieve precise rotational movement [11][12][13]. As shown in Figs.…”

“…Among the many elastic joints available, the cross-spring is one of the most precise rotational joints. It can be applied in various fields which require precise rotational motion [11][12][13]. Structurally, the cross-spring is composed of two orthogonally crossed thin plates that can link fixed and moving parts.…”

Hinge pivot for disk drive

“…Other methods using a bearing-less pivot have been described in numerous patents (Lawson 2003;Heath 1996;Schuize 1994). Flexural pivot for use in hard disc drive was investigated by He (2003) and Chainer (1991). Although the intend proposed by the above authors was to provide a lower friction torque pivot and to eliminate the need for ball bearings for cost reduction.…”