In this paper, a new modeling of a fine actuator for optical pick-up has been proposed and multiobjective optimization of it has been performed. The fine actuator is constituted of the bobbin which is supported by wire suspension, the coils which wind around the bobbin, and the magnets which cause the magnetic flux. If current flows in the coils, magnetic force is produced and then it is balanced with spring force of wire, so the bobbin is positioned.
The conventional model assumes the system as simple second order system with spring, mass and damper. This approach can analyze the dynamics easily. However, it is unable to consider the length and amount of damping because the distributed damper is regarded as a lumped damper. In addition the high frequency characteristics and the effects of damping to its characteristics cannot be described since higher resonant mode was not included.
In this model the transfer function from input voltage to output displacement of bobbin has been obtained so that we can describe this electromagnetic and mechanical system. Wire suspension is regarded as a continuous Euler beam, damper as distributed viscous damping, and bobbin as a rigid body which can move up- and down-ward motion only. According to the model, the high frequency dynamic characteristics of the fine actuator can be known and the effect of damping can be investigated while the conventional second order model cannot.
In multiobjective optimization, two objective function has been chosen to maximize the fundamental frequency and the sensitivity with respect to input voltage of the actuator. Pareto's optimal solutions have been obtained using ε-constraint method. These objective functions can satisfy the requrements in the optical pick-up technology of next generation i.e., the higher access speed and the smaller tracking error.
