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

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.