JPH0431415U

JPH0431415U -

Info

Publication number: JPH0431415U
Application number: JP7110490U
Authority: JP
Priority date: 1990-07-05
Filing date: 1990-07-05
Publication date: 1992-03-13

Description

[Brief explanation of the drawing]

第１図は本考案の一実施例を示すブロツク図、
第２図は非点収差法による光学系の構成図、第３
図は従来例のブロツク図、第４図は光検出器の受
光面上のビームスポツトの形状変化を示す図であ
る。６……光検出器、７，８……加算器、９……差
動アンプ、１０……駆動回路、１１，１３，１４
……可変抵抗器、１５……スイツチング手段、１
６……制御回路。 FIG. 1 is a block diagram showing an embodiment of the present invention.
Figure 2 is a configuration diagram of the optical system using the astigmatism method, Figure 3
This figure is a block diagram of a conventional example, and FIG. 4 is a diagram showing changes in the shape of a beam spot on the light receiving surface of a photodetector. 6... Photodetector, 7, 8... Adder, 9... Differential amplifier, 10... Drive circuit, 11, 13, 14
... Variable resistor, 15 ... Switching means, 1
6...Control circuit.

Claims

[Claims for Utility Model Registration] A photodetector consisting of four elements arranged close to each other and independent of each other, and a light beam that has passed through the recording surface of the information recording disk, is directed onto the light receiving surface of the detector with astigmatism. In the focus servo device, the focus servo device includes an optical system that guides the four elements, and generates a focus servo error signal based on each output signal of the four elements. an adder for adding the outputs from the elements; a variable resistor connected in parallel to one output of the adder; switching means connected to the variable resistor; A differential amplifier that takes the difference from the output from another adder, a focus servo drive circuit that drives a lens using the output from the differential amplifier, and a focus servo drive circuit that drives the switching means when a tracking servo loop is opened and closed. A focus servo device characterized by comprising a control circuit that sends out switching outputs.