Hard disk drive with voltage-driven voice coil motor and model-based control

In this paper, we describe the voice coil model-based control (VCMC), a new solution for driving the voice coil motor (VCM) in hard disk drives (HDDs), in which the usual current driver for the VCM has been replaced by a voltage driver. The VCMC replicates the behavior of a current loop by using a model of the VCM and its driver, including the saturation of the power stage. Since VCM resistance may change by 30% during HDD operations, the model used by VCMC must be adapted accordingly, in order to achieve the same performance as the standard current driver. This paper presents a pair of online estimation procedures used to get the value of the VCM coil resistance during seek and track following, respectively. It will be shown that both procedures are quite accurate in estimating variations of VCM resistance and their output can be used to perform online tuning of the VCMC. Experimental results show that the servo performance with the adaptive VCMC is not affected by resistance variation and it is equivalent to that of the standard current driver.