This paper presents the self-sensing control of a microactuator for hard disk drives. The microactuator uses a PZT actuator pair installed on the suspension assembly. The self-sensing microactuator forms a combined sensing and actuation mechanism. Direct velocity feedback and positive position feedback are used in this paper. Our experimental results show that both strategies are effective in suppressing vibrational modes and successfully demonstrate the feasibility of using a self-sensing actuator on an HDD suspension assembly. 1. Introduction A suspension assembly in a hard disk drive (HDD) is subject to excitation by many disturbances, including the airflow due to the rapidly spinning disks, and noncircular track motion of the head and slider due to resonance in the components. A servo system that can cope with these problems requires a very high servo bandwidth and position error signal sampling frequency. In conventional servo systems, the sampling frequency is limited by data storage efficiency. The desire to more effectively suppress the effect of disturbances has led many researchers to propose the addition of more sensors and actuators. One example which has been proposed is to use a piezoelectric actuator on the suspension in a dual-stage system with one of the two strips as the sensor and the other as the actuator [1, 2]. This, however, reduces the effectiveness of the actuator by half and is not efficient. An alternate approach is to use it as a self-sensing microactuator [3–9], which is the subject of this paper. For dual-stage servo system, the performance of self-sensing actuator systems exceeds that of other vibration compensation systems. We implemented two active strategies in order to experimentally demonstrate the effectiveness of a self-sensing system in structural vibration control. The strategies are direct velocity feedback (DVF) and positive position feedback (PPF). DVF, also known as strain rate feedback (SRF) has been used in the active damping of a flexible space structure [10]. In DVF, the structural velocity coordinate is fed back to the compensator and the compensator velocity coordinate multiplied by a negative gain is applied to the structure. DVF has a wide active damping region and can stabilize more than one mode given sufficient bandwidth. In PPF, the structural position coordinate is fed directly to the compensator where a scalar gain is applied and the result sent to the structure [11, 12]. PPF offers quick damping for a particular mode provided the modal characteristics are known. PPF is also easy to implement.
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