JPH0660969B2 - Optical disc player-lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION a) Field of Industrial Application The present invention relates to a lens for use in an optical disc player, which can be manufactured economically and can adopt a simple lens mount because of its light weight.

b) Prior Art Optical discs are known which consist of a rigid transparent disc with a reflective coating on the side facing away from the player's reading head. Non-reflective dots are created in the reflective coating to record information. The record is read by directing a laser beam through a transparent disc to a reflective coating and detecting the reflected energy, so that the dots are detectable due to their low reflectivity.

The laser beam is focused by the lens on the plane of the reflecting surface and the reflected energy is focused on the sensor by the same lens. Many lenses known for optical disc players are composed of multiple elements. The laser beam has to be very accurately focused on the reflecting surface and the player has to maintain said exact focus as the disk spins in front of the lens at high speed. The disk may not be flat at all,
There is a slight inclination in the rotation amount of the disk, and the surrounding conditions may change. All these factors make it necessary to adjust the focus, which is done by moving the lens.

c) Problems to be Solved by the Invention Usually, focus adjustment needs to be performed extremely quickly, which requires high speed acceleration. The force required to generate acceleration is a function of the mass being accelerated. Lenses consisting of multiple elements have a high degree of mass, which requires large forces to accelerate them. The present invention seeks to solve the aforementioned problems, and at the same time to reduce the mass of the lens to be accelerated by providing a single element lens with excellent resolution.

d) Means for Solving the Problems In the present invention, the refractive index N800 is 1.492, and the Atsube V number is 57.4.
The problem is solved by providing a single biconvex element that is Both sides of the element are aspherical surfaces in accordance with the following equation.

X is the distortion of the aspherical surface from the flat reference surface at the radial distance Y from the axial center of the lens, e) Working Example of the Invention As shown schematically in the drawing, the player lens for the optical disc 11 consists of a single element 13.
The lens element 13 is a biconvex lens whose surfaces 1 and 2 are aspherical surfaces.

The aspherical surface can be defined by the following equation.

The above equation defines each surface with respect to surface distortion X at a half aperture distance Y from the lens axis. The constant C is the curvature of the surface at the apex of the lens and is equal to the reciprocal radius of curvature at the apex.

The thickness of the element is 3.386 mm and its perval (P
etzval) sum is 0.007651. It has a 1.00 degree half-angle field of view.

The refractive index N800 of the element is 1.492. Atsube V number is 57.4. The element is formed from polymethylmethacrylate.

The optical disc 11 has a thickness of 1.2 mm and has a reflective coating on the surface 4 for holding information. Disk 11 has an index of refraction of 1.494, Ohara B
It is made of K-9 glass. The information is in the form of dots created by a laser that disrupts the reflectivity of the coating.

The proper spacing of the lens elements from the disk face 3 measured from the lens axis 15 is 2.00 mm. With this spacing, surface 4 is at the focal point of the element.

FIG. 3 shows the aberration curve of the lens according to the present invention.

In this embodiment, the element 13 is attached to a tire ring 17 made of plastic material. Ring 1
7 has a circular cylindrical surface 19 which is the element 13
It has a coaxial relationship with the axis 15 of. The ring is molded on an element, the molding process of which causes the axis of the lens to be positioned coaxially with the cylindrical surface of the mold cavity forming surface 19. Thus, the cylindrical surface, which is coaxial with the axis of the lens element and which is fixed in relation to the axis, is economical without any restrictions on the process of actually forming the lens element. To be achieved.

In this example, a diaphragm 21 with a 4.32 mm aperture is located 0.304 mm from surface 1 of element 13.

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. The lens described above is suitable for this region of the spectrum.

f) Effects of the Invention As described in the previous section, the present invention provides a single element lens that can be used in an optical disc player. The present invention weighs much less than the known multi-element player lens, 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 description of drawings]

FIG. 1 is a schematic view of a lens according to the present invention and a part of an optical disk in an operative relationship with each other, FIG. 2 is a view showing the lens of FIG. 1 provided with a plastic tire, and FIG. 3 is an aberration curve of a lens according to the present invention. 1 ... the first surface of the lens, 2 ... the second surface of the lens, 1
1 ... Optical disc, 13 ... Lens element.

Claims (1)

[Claims] 1. A refractive index N800 having an Abbe V number of 57.4.
Is an optical disc player lens which is composed of one biconvex element having a diameter of 1.492, and whose both surfaces are aspherical surfaces that meet the following equation, where X is a flat surface at a radial distance Y from the axial center of the lens. An optical disc player lens which is a distortion of an aspherical surface from a reference surface and has the following numerical values.