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(2)聚焦伺服系统①聚焦误差检出。相对于碟片移动物镜时,聚焦误差电压沿正方向增大,在约2毫米距离附近(相对碟片而言)急剧地从正变为负,然后再次增大。而且移离物镜时误差电压则变为零,此2毫米附近的斜率变化成为定焦聚所必须的信号。为使聚焦伺服电路动作,需要有定距离前的访问动作、增益调整与相位补偿等。聚焦误差电压与碟片距离的关系如图15所示。②聚焦伺服。 A.聚焦访问(对焦点的搜索动作)概要
(2) focus servo ① focus error detection. When moving the objective with respect to the disc, the focus error voltage increases in the positive direction, sharply changes from positive to negative (and with respect to the disc) about 2 mm and then increases again. When the objective lens is moved away from the objective lens, the error voltage becomes zero, and the slope change near 2 mm becomes a necessary signal for the fixed focus. In order to focus servo circuit action, you need to have a distance from the previous visit to action, gain adjustment and phase compensation. Focus error voltage and the relationship between the disc distance as shown in Figure 15. ② focus servo. A. Focus access (focus search action) summary