Position Error Predictions of a Hard Disk Drive Undergoing a Large Seeking Motion With Shock Excitations

In this paper, we present numerical simulations to predict position errors of a hard disk drive (HDD) undergoing a long seeking-and-settling process while experiencing a shock excitation. The HDD model for simulations consists of a rotating spindle motor carrying multiple disks, a stationary base with a top cover, and a swinging head-stack assembly (HSA). The rotating part, stationary part, and swinging HSA are connected to one another via fluid-dynamic bearings, pivot bearings, and air bearings. The seeking-and-settling process consists of four segments: acceleration, coasting, deceleration, and settling. A 2-ms shock excitation is applied to each segment of the seeking-and-settling process, respectively, to evaluate severity of the shock excitations to position errors. Both linear and angular shock excitations are considered. Simulation results lead to the following significant conclusions. First, shock excitations generally result in two types of response: spindle vibration [e.g., half-speed whirls or (0,1) unbalanced modes in the form of rocking] and HSA vibration (e.g., torsional vibration of the voice coil or bending of the suspension arms). Moreover, spindle vibration response usually appears with large amplitude (per unit g) but damps out quickly due to its large damping. In contrast, HSA response usually appears with small amplitude (per unit g) but decays slowly due to its small damping. As a result, shock excitations applied near the beginning of the seeking-and-settling process are less detrimental because the larger spindle response has enough time to damp out before the heads settle on the desired tracks. In contrast, shock excitations applied to the end of the seeking-and-settling process tend to present large spindle response leading to significant position errors. In this case, the ability to rapidly reduce the position errors relies on performance and properties of the fluid-dynamic spindle motor.