Disc positioning device

A disc positioning device for positioning a disc having a center opening with respect to a spindle for driving the disc for rotation by bringing the center axes thereof into alignment with each other. An adapter in the form of a hemispherical body of a diameter greater than that of the center opening of the disc is mounted on the spindle in such a manner that the center of a spherical body from which the hemispherical body of the adapter is severed coincides with the center axis of the spindle at all times. The adapter is urged by a spring to be biased with the center thereof serving as the center of rotation.

FIELD OF THE INVENTION 
This invention relates to positioning devices for a rotary disc of an audio 
record player, a video disc player, etc., and more particularly it deals 
with a disc positioning device of the type having an adapter interposed 
between the head of a spindle and the opening in a disc for bringing discs 
having openings of different diameters into alignment with the spindle by 
fitting the latter into the former.

DESCRIPTION OF THE PRIOR ART 
FIG. 1 shows a disc positioning device of the prior art in a sectional 
view, in which a spindle 1 is adapted to be fitted in an opening formed in 
a disc 2. In this type of disc positioning device, difficulties would be 
experienced in bringing the center 3 of the spindle 1 into alignment with 
the center 4 of the disc 2 if the disc 2 shows variations in the diameter 
of the opening. 
FIG. 2 shows, in a sectional view, Japanese Utility Model Laid-open No. 
33407/78 which represents an improvement in the prior art shown in FIG. 1. 
As shown, an adapter 6 capable of moving vertically in aliding movement 
with respect to the spindle 1 by the biasing force of a spring 5 and 
tapering in its outer periphery to accommodate variations in the diameter 
of the opening of the disc 2 is provided to bring the spindle into 
alignment with the opening in the disc. In the device, it is desired that 
the gap between the opening in the adapter 6 for receiving the spindle 1 
and the spindle 6 be eliminated. However, it is necessary that a gap of a 
large size be provided in view of variations in the size of the gap 
inevitably occurring in production and there is a difference in the 
coefficient of thermal expansion between the spindle 1 and adapter 6. 
Also, the gap increases in size with time as wear is caused on the adapter 
and the spindle during use. Thus, difficulties have been experienced in 
obtaining accurate positioning of the disc by the device of the prior art. 
SUMMARY OF THE INVENTION 
This invention has been developed for the purpose of obviating the 
aforesaid problem of the prior art. Accordingly the invention has as its 
object the provision of a disc positioning device capable of bringing the 
center axis of a spindle into alignment with the center of a center 
opening in the disc without any trouble. 
The aforesaid object is accomplished according to the invention by 
providing a mechanism whereby a deviation in axis caused by a gap in size 
between openings in an adapter and the spindle can be accommodated by 
mounting the adapter on the spindle in a tilting position and a deviation 
in axis caused by a difference between the diameter of the adapter and the 
diameter of the center opening of the disc can be accommodated by 
imparting to the adapter a hemispherical body centered at a point 
equidistantly spaced apart from end portions of one of the openings in the 
hemispherical body and having a diameter greater than that of the center 
opening of the disc. 
The adapter according to the invention has a curved surface formed by the 
hemispherical body and larger in diameter than the center opening of the 
disc and formed inside the hemispherical body with a first opening of a 
diameter greater than the diameter of the spindle having opposite ends 
forming two circles connected together by a straight line bisected at the 
center of the hemispherical body, and a second opening connecting one end 
of the first opening to the inclined or curved surface of the 
hemispherical body. 
Means is provided for biasing the adapted to force same against the disc 
and also for rotating the adapter about a center which is the center of 
the semispherical body. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the invention will now be described by referring 
to FIGS. 3 and 4. FIG. 3 is a sectional view taken along a plane including 
the center axis of a spindle 1, and FIG. 4 is a perspective view. As 
shown, the spindle 1 and a disc 2 are similar to those shown in FIG. 2. 
The numeral 8 designates an adapter according to the invention in the form 
of a hemisphere of a diameter greater than that of an opening in the disc 
2 left over by removing a part of a lower half portion of a spherical 
body. The adapter 8 of the hemispherical body is formed in the central 
portion with a vertical through hole or a first opening 9 of a diameter 
greater than the diameter of the spindle 1, and a hole or a second opening 
10 greater in diameter than the first opening 9 and located thereon which 
provides end portions 11 and 12 of the first opening 9 equidistantly 
spaced apart from a center 13 which is the center of the spherical body 
from which the hemispherical adapter 8 is severed. The numeral 14 
designates a spring mounted at one portion of the undersurface of the 
semispherical adapter 8 to urge the adapter to move upwardly at one end 
portion thereof when the adapter 8 is mounted on the spindle 1 so that the 
adapter 8 will tilt into contact with the spindle 1 at the upper and lower 
ends of the openings of the spindle 1. 
The first opening 9 of the adapter 8 is greater in diameter than the 
spindle 1, but the center 13 of the spherical body from which the 
hemispherical body 8 is severed is located on the center axis of the 
spindle 1 at all times because the adapter 8 is in contact with the 
spindle 1 when the latter is in a tilting position, thereby eliminating 
any deviation of the center axis of the adapter 8 from that of the spindle 
1. The adapter 8 tilts while its center is located at the center 13 of the 
spherical body, so that points of contact on the adapter 8 with the edge 
of the opening in the disc 2 are equidistantly spaced apart from the 
center 13 of the spherical body. Thus the center axis of the disc 2 
coincides with that of the spindle 1. 
In the embodiment shown and described hereinabove, no means is provided for 
avoiding dislodging of the adapter 8 upwardly of the spindle 1 in the 
drawings. However, if necessary, the spindle 1 may be formed with a flange 
of a diameter greater than that of the second opening 10 of the adapter 8 
to serve the aforesaid purpose. 
From the foregoing description, it will be appreciated that the invention 
enables the center axes of the spindle and the disc to be brought into 
alignment with each other that has hitherto been impossible in the prior 
art, without varying the number of parts necessary for the construction. 
This is conductive to minimization of wow and flutter in the basic 
frequency of rotation of the disc.