Vibration of rotating-shaft HDD spindle motors with flexible stationary parts

Dropping, striking, or bouncing a hard disk drive (HDD) against a hard surface can damage it internally without external evidence of damage. Contact with a hard ground will lift the slider off the disk surface and then slap back on the surface. A drive that is subjected to this type of shock may fail on initial use or the reliability of the drive may degrade over time. Therefore, industry has a lot of interest on the shock conditions that cause a slider to lift off the disk surface. Finite element software such as ANSYS/LS-DYNA is often used to analyze this shock problem. However, this method consumes a great amount of time. It is also difficult to perform design parameter studies because it requires re-analysis of the model of the entire HDD system when certain design variables are changed. This paper presents a flexible multi-body dynamics formulation to analyze the shock problem of non-operating HDDs. Governing equations of motion of the voice coil motor (VCM)-actuators assembly and the disks-spindle system are derived using a Lagrangian formulation. By introducing constraint equations between the slider and the disk surface, the shock response of the whole HDD system has been obtained. Numerical results show that the method is reasonable and the acceleration amplitude which makes the slider lift off can be determined in a significantly shorter time than by the conventional approach. Finally, the effect of drive parameters on shock resistance, such as shock duration and slider resting location are analyzed.

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Shock analysis of non-operating hard disk drives based on a multibody dynamic formulation

Gao

Yap

Ying

et al. 2005

Microsyst Technol

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Vibration of hard disk drive spindle systems with distributed journal bearing forces

Jintanawan

2005

Microsyst Technol

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This paper is to analyze vibration of fluid dynamic bearing spindles with distributed journal bearing forces. The dynamical model is developed to predict the transverse vibration of the disk-spindle systems in HDD where an aspect ratio of the bearing width to the shaft length is significant and the shaft is likely flexible. In such spindles the journal bearing functions as a continuous support, providing the distributed restoring and damping forces, and is therefore modeled as distributed linear spring and damping forces through distribution functions of dynamic coefficients. Vibration analysis reveals that the spindle model with distributed bearing forces predicts the same natural frequencies for all transverse modes but higher modal damping of the rocking modes, when compared to the values predicted by the conventional model with discrete bearing forces. The difference in damping prediction is clearer for the flexible-shaft spindle whose ratio of the bearing width to the shaft length becomes larger.

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Finite element modal analysis of a spinning flexible disk-spindle system in a HDD considering the flexibility of complicated supporting structure

Jang

Han

2005

Microsyst Technol

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The free vibration of a spinning flexible diskspindle system in a HDD considering the flexibility of complicated supporting structure is analyzed by FEM and substructure synthesis. The spinning flexible disk is described using Kirchhoff plate theory and von Karman non-linear strain, and its rigid body motion is also considered. It is discretized by annular sector element. The rotating spindle which includes the clamp, hub, permanent magnet and yoke, is modeled by Timoshenko beam including the gyroscopic effect. The stationary shaft is also modeled by Timoshenko beam. The flexible supporting structure with a complex shape which includes the stator core, housing and base plate is modeled by using a four-node tetrahedron element with rotational degrees of freedom to satisfy the geometric compatibility at the interface node between the one-dimensional (1-D) beam element and the 3-D solid element. Rigid link constraint is imposed at the interface area between shaft and housing to describe the physical motion at this interface. The global matrix equation obtained by assembling the finite element equations of each substructure is transformed to the state-space matrix-vector equation, and the associated eigenvalue problem is solved by using the restarted Arnoldi iteration method. The validity of this research is verified by comparing the numerical results of the natural frequencies and mode shapes with the experimental ones. This research shows that the flexible supporting structure as well as the rigid link constraint between shaft and housing play an important role in accurately predicting the natural frequencies.

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Vibration of rotating-shaft HDD spindle motors with flexible stationary parts

Cited by 31 publications

References 3 publications

Shock analysis of non-operating hard disk drives based on a multibody dynamic formulation

Shock analysis of non-operating hard disk drives based on a multibody dynamic formulation

Vibration of hard disk drive spindle systems with distributed journal bearing forces

Finite element modal analysis of a spinning flexible disk-spindle system in a HDD considering the flexibility of complicated supporting structure

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