Feedforward Decoupling Control Design for Dual-Actuator System in Hard Disk Drives

Abstract

The dual-actuator hard disk drive (HDD) with two actuators mounted in the diagonal corners of the baseplate allows faster data access with relatively slower spindle speed. However, the mechanical interaction between the actuators tends to affect the head positioning accuracy. In this paper, the dual-actuator structure is formulated as a dual-input dual-output (DIDO) system and then identified in frequency domain. Based on the interaction models, the feedforward decoupling control (FDC) is developed to compensate for the vibration due to interaction. Experimental results on a dual-actuator prototype demonstrate that the position error signal (PES) value due to interaction is reduced by 72% even under the severest condition.

An extended approach of inverted decoupling

“…It is rarely mentioned in the literature [11], [21], [22], [23], and in those cases, it is only applied to TITO processes using the scheme depicted in Figure 2. In this case, it is possible to keep the same apparent process of ideal decoupling while using the simple decoupler elements of simplified decoupling [11].…”

Practical advantages of inverted decoupling

“…It is rarely mentioned in the literature, but it is very easy to implement when it can be applied [19]. Inverted decoupling scheme for a 2x2 process is shown in Figure 1b.…”

Improvement on an inverted decoupling technique for a class of stable linear multivariable processes

“…To reduce these interactions, some work in the literatures (for example [1][2][3]) focuses on the multi-loop control structure because of its simple configuration. The authors of some of the literatures (for example [4][5][6][7][8][9][10][11][12][13]) are attracted by the decoupling control structure which has been commonly used in many distillation industrial processes [8,9]. The decoupled closed-loop response of each loop is the same as it would be if other loops were on manual or automatic control on the assumption that there is no loop failure.…”

“…Although Waller et al [6] put forward a modified simplified decoupling approach, the derived decoupled process still cannot achieve the simplest form. The inverted decoupling structure, also named feedforward decoupling control [11], avoids the disadvantage of the simplified decoupling and achieves the purpose of the ideal decoupling. Furthermore, this decoupling structure offers additional benefits [10]: (i) it is easier to deal with the initialization problem which consists in finding the right controller output values to allow bumpless switches between the manual and automatic modes; (ii) the saturation of the manipulated variables is directly taken into account in the inverted decoupling structure.…”

“…Wade [13] discussed the design of the decoupler, and stated a condition that the processes have to meet in order to guarantee the nominal stability of the inverted decoupling structure. On the basis of the work of [13], Zheng et al [11] applied the inverted decoupling control to the dual-actuator hard disk drive system. The experimental result shows that the interaction of this two-input-two-output (TITO) system is reduced by 72%.…”