Optical device for reading information

摘要

An optical playback or recording device is equipped with mass-unbalance detection means ( 20 ) for detecting unbalance on the record carrier ( 2 ). Mass-unbalance causes vibration and sound in the optical device when the record carrier ( 2 ) is rotated at a relatively high speed. When mass-unbalance is detected, the speed may be reduced to reduce the vibration and sound in the optical device. The mass-unbalance detection means ( 20 ) performs the following steps to detect mass-unbalance: a) determining the maximum value U_max1 of the actuator control signal (AS) at a rotational speed Omega₁; b) determining the maximum value U_max2 of the actuator control signal (AS) at a rotational speed Omega₂; c) comparing Formula (I) with Formula (II). If these values are substantially equal, then the effect of mass-unbalance is small, otherwise the effect of mass-unbalance is too great and the speed may have to be reduced $\begin{array}{cc}\frac{U_{\max 1}}{{\mathrm{omega}}_1^2}\mathrm{with}\frac{U_{\max 2}}{{\mathrm{omega}}_2^2}.& \left(I\right)\end{array}$