In optical disc system, a tracking system consists of a coarse actuator and a fine tracking actuator. This, 2-stage actuator, requires many devices in order to obtain large stroke and precisional displacement. Moreover, the moving parts become heavy because of the complicated configuration.
In this paper, one dimensional new tracking actuator is designed and constructed.
A System design is carried out as followings:
Firstly, the Voice Coil Motor is used as a basic drive mechanism. The permeance method is used to analyze and to design VCM for large driving force. Also, a magnetic field simulation is done to verify magnetic analysis in the permeance method. And it is proved experimentally that magnetic flux density is measured by gauss meter instrument.
Secondly, the focusing spring is designed with relation to stability of system. The spring design is needed since a positioning and a forcing point are different. It is found that the focusing stiffness has to be low for dynamic sensitivity and the tracking stiffness has to be high for stable condition when actuator moves in high speed.
Thirdly, the friction identification is carried out. Since friction is one of the dominant error sources, it must be reduced to a reasonable limit. The sensor gain and the control gain are limited even though they can reduce the friction effect as possible as high because of stability problem. So, the plastic coating is used to reduce friction when the system is made.
The actuator is constructed based on above design method and controlled.
The dynamic characteristics of the system are experimented by an analyzer instrument. It shows the satisfactory tracking characteristic with the desirable focusing one. Also, PD control is applied for various input signals. It results in below $\pm 0.1mm$ error resolution. These errors are raised by two dominant error sources, that is, the friction and the inertia effects. The experiment results show that the friction effect is a more important error source than inertia effect.
