JPS6266217A - Optical disc player lens - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION a) Industrial Field of Application The present invention can be manufactured economically and is lightweight, so that a simple lens macanto can be employed. This invention relates to lenses used in optical disc players.

b) Prior Art Optical discs are known which consist of a rigid transparent disc with a reflective coating on the surface of the player remote from the read head.

Non-reflective dots are created in the reflective coating to record information. The record is read by directing a laser beam through the transparent disc onto the reflective coating and detecting the reflected energy so that the dots are detected due to the low reflection return.

The laser beam is focused by a lens onto the plane of the reflective surface and the reflected energy is focused by the same lens onto the sensor. Many lenses known for use in optical disc players are composed of multiple elements. The laser beam must be focused very precisely onto the reflective surface, and the player must maintain said precise focus as the disc rotates rapidly in front of the lens. The disc may not be completely flat,
There is a slight inclination depending on the amount of rotation of the disk, and the surrounding conditions may change. All these factors create the need to adjust the focus, which is done by moving the lens.

C) Problem that the invention seeks to solve Focus adjustment usually needs to be done very quickly.

This VC requires high speed acceleration. The force required to produce acceleration is a function of the mass being accelerated.

Lenses consisting of multiple elements have a high degree of mass requiring large forces to accelerate them. The present invention is an attempt to solve the above-mentioned problems, and at the same time aims to reduce the quality flc of the lens to be accelerated by providing a single element lens with excellent resolution.

d) Means for Solving the Problem The present invention solves the problem by providing a single biconvex element with a refractive index N800 of 1.492 and an Abbe V number of 57.4. Both sides of the element are aspherical surfaces that conform to the following formula.

X is the degree of curvature of the aspheric surface from the flat reference surface at the radial distance Y from the axis of the lens, where Surface 1 Surface 2 G = 0.55,4021 -0.1557560 = o, o -20, 4938259D=-〇, 2909441X10-20゜DK=-0,51
65409 x 10”30, OF=0.50758
B6X1[1-'o, DG=-0,1599892x
10-'o,.

e] Example of operation of the invention As schematically shown in the drawing, the player lens for the optical disc 11 consists of a single element 16.

Said lens element 16 is a biconvex lens in which both surfaces 1, 2 and 6 are aspherical.

The aspheric surfaces can be defined by the equation below, which defines each surface in terms of the surface distortion, X, at a half-aperture distance, Y, from the axis of the lens.

The constant C is the curvature of the surface at the apex of the lens.

At the vertex, the radius of curvature is equal.

C: 0.554021 -0.15575
to 60 = 0.0 -20.4938
2390 = -0,2909441Xl 0-20.
0E = -0,5165209X 10-30.0F
= 0.5075886x10-' C1,.

G=-0, 1599892x10-' O, [] The thickness of the elementary member is 3.586 mm, and the thickness of the seventh plate'/
The (Petzval) sum is 0.007651. It has a half-angle field of view of 1.00 degrees.

The refractive index N800 of the element σ) is 1.492. Atsube's V number is 57.4. The element is formed from polymethyl methacrylate, with an optical disc thickness of 11σ). It is 2 mm,
It has a reflective coating on surface 4 to retain information. The disk 11 has a refractive index of 1.4940 O'Hara (O
hara) is made of BK-9 glass. The information is in the form of dots created by a laser that disrupts the reflective properties of the coating.

From the surface 6 of the disk, the lens σ) axis 15 to ff1
13 Appropriate 1% of the fixed lens element! 2.
o.

If the distance is in millimeters, then 4 will be at the focal point of the element.

In this embodiment, the element 16 is mounted on a tire-like ring 17 made of plastic material. ring 1
7 has a circular cylindrical surface 19'.

The cores are coaxial with the axis 15 of the element 1'5. The ring is molded into an element, the molding process being such that the axis of the lens is located in a coaxial relationship with the cylindrical surface of the cavity of the mold forming element 19. In this way, there is a coaxial edge relationship with the axis of the lens element,
Moreover, the cylindrical surface fixed in relation to the axis can be economically achieved without imposing any restrictions on the process of actually forming the lens element.

In this embodiment, a diaphragm 21 with an aperture of 4.52 mm is used as the element 16 from 1 to 0.
As is well known, video disc players include a laser operating in the infrared region of the spectrum as an energy source for reading the disc. Appropriate for this region of the spectrum.

f) Effects of the Invention As explained in the previous section, the present invention provides a single element lens that can be used in an optical disc player. The present invention is much lighter in weight than known multi-element player lenses and therefore requires less energy to move for focusing. The lens of the present invention not only has a low mass, but also has high resolution.

[Brief explanation of drawings]

FIG. 1 is a schematic illustration of a lens according to the invention and a portion of an optical disc in operative relationship with respect to each other; and FIG. 2 shows the lens of FIG. 1 with a plastic tire. Illustrated. DESCRIPTION OF SYMBOLS 1... First surface of lens, 2... Second surface of lens, 11... Optical disc, 15...
Lens element, (4 others) FIG, I FIG, 2 Procedural amendment dated December 16, 1986 2, Name of the invention Optical disc player Lens 6, Relationship with the person making the amendment Patent applicant address Name ( 707) Eastman Kodak Company 4, Agent 6, Contents of Amendment 1. The attached drawing is referred to as Figure 3 of this application. 2 Change the line next to "It comes to..." on page 6, line 13 of the specification and insert the following. "Fig. 3 shows the aberration curve of the lens according to the present invention.j 3. "and" on page 8, line 5 of the specification is deleted, and "Fig. ” was corrected. 4. Page 8 of the specification Change the line after the line M) and insert the following. "Figure 3 is the aberration curve of the lens according to the present invention."

Claims (1)

[Claims] It has an Atsube V number of 57.4 and a refractive index N800 of 1.4.
92, and both surfaces of the lens are aspheric surfaces conforming to the following equation, where X is a flat reference at radial distance Y from the axis of the lens. An optical disc player lens which is an aspherical distortion from a surface and has the following numerical values. X=CY^2/{1+√[1-(K+1)C^2Y^2
]｝+DY^4+EY^6+FY^8+GY^1^0 ￥ Surface 1 Surface 2
￥ C=0.354021 -0.1
557360 K=0.0 -20.4
938239 D=-0.2909441×10^-^2 0.0 E=-0.5163209×10^-^3 0.0 F=0.5075886×10^-^4 0.0 G=-0. 1399892×10^-^4 0.0