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The disk rotation speed of optical disk drives (ODD) has been increasing rapidly to achieve high data transfer rates. High servo bandwidths for focusing and tracking actuator are required to follow dynamic disturbance by high rotation speed in ODD. However, the servo bandwidth is significantly limited by some vibration modes which are induced by the flexibility of the moving part. In this work, the vibration modes affecting the bandwidth of actuators are shifted to high frequency range and suppressed by modifying the FE model which is used to analyze the motion of the actuator. Some local dimensions of the lens holder, which is included in the moving part, are selected as design variables to increase the stiffness without changing the material properties. Selected modal frequencies of the moving part are raised about 10%, while the performances of actuator such as DC and AC sensitivities are hardly affected by the modification.

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In this paper, a swing-arm-type dual positioning mechanism using a voice coil motor (VCM) and bimorph PZT actuators is proposed for the possible application to the future optical disc drive actuator. A VCM is used as a coarse motion actuator, and a set of piezoelectric actuators is used for fine motion. The two pairs of PZT actuators are arranged in parallel and are carefully designed to deflect in 'S' shape such that tension and compression forces are generated simultaneously and thus the hysteresis is minimized. The static and dynamic analyses are performed and the parameter studies on the key dimensions of the set of PZT actuators are investigated. For fast seeking motion, time optimal control scheme combined with PD algorithm is adopted for the fast seeking motion of VCM. Positive position feedback (PPF) control is used to suppress residual vibration for the PZT actuator beams by activating it at the end of VCM swing motion. The feasibility of the suggested actuator system and the control scheme is demonstrated through simulations and experiments. IntroductionIn today's optical disk drives (ODDs), a worm gear or a rack-and-pinion is used as rotary-to-linear translation mechanism to move the pickup unit. This mechanism has a good power transmission ratio, but inherently produces noise and needless vibration, which is one of the obstacles to decrease the access time of the optical disk drive equipped with a rather heavy optical unit. Further, the objective lens is supported by a 4-wire suspension spring, and thus there may exist coupling modes between tracking and focusing directions. These coupling modes could lead to the misalignment of the optical axes. In addition, the conventional actuator is difficult to be fabricated in a small form factor, because the fabrication process is rather complex and it is composed of many parts. The currently used pickup actuator mechanism so far meet with good performance for the present commercial drives. However, we may expect that such mechanism will become unsuitable for the future optical disk drive, especially, for the small form factor drive.On the other hand, HDD uses VCM as a single swingarm-type actuator, which is simple in structure compared to ODD actuator and is advantageous for small form factor drive, for example, IBM Microdrive. However, as the track density of HDD is continuously increased, many researchers have recently suggested dual-type actuators for HDD with a secondary PZT, electrostatic, or electromagnetic actuator (Evans et al., 1999), and the one with PZT seems to be nearest to commercialization.One of the major drawbacks of piezoceramic actuators, however, is the accuracy degradation due to the hysteresis effect and the drift. Many efforts have been made to improve the hysteresis behavior of piezoceramic actuators. The schemes can be divided into three categories: the use of electric charge to drive piezoceramic actuators instead of applied voltage, the use of feedforward nonlinear models in driving the actuators, and the use of closed-loop control ...