Hard disk drive (HDD) is a standard component of computer systems for data storage. With the advance of technology, increase of capacity and reduction of price, it is now used more and more in non-traditional computing systems, such as camcorders, portable video and music players, etc. These new applications have different emphasis on HDD performance compared to computers. They might not require very large storage capacity, super fast read access, but need high reliability under operational and non-operational conditions. In particularly, for portable devices, HDD has to survive common non-operational shocks during the daily usage of the devices. One design to improve HDD non-operational shock resistance is to unload read-write heads from media to a ramp after power off instead of leaving them on the medial at a special landing zone. A latch mechanism, such as the pawl latch studied in this paper, is then used to lock them on the ramp. During shock events, all the heads are well separated or limited by the ramp to protect them from hitting each other. Since the heads are off the media, they will not contact the media and cause data loss either. The reliability of load/unload (L/UL) drives, however, does not come free. Other than some design changes, which tend to increase cost, extra care also needs to be taken to load the heads to the media or unload them from the media to the ramp. This paper takes a close look at the inertia/magnetic latch non-operational shock performance and the actuator load process. Mechanical, servo and electronic systems are considered together to create a closed-loop simulation model. The effects of voice coil motor K_t drop off, magnetic latch torque bias, IR sensing circuit on load velocity variation are examined. The physical insights provided in the paper should facilitate the design of HDD.
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