Holographic disk mounting system and method

A holographic disk mounting system and method is disclosed utilizing a compressible O-ring which eliminates the clearance between the spin motor shaft and the holographic disk. The holographic disk has an axial bore with a diameter slightly greater than the diameter of the spin motor shaft. A compressible O-ring is placed around the spin motor shaft and then the holographic disk is mounted thereon with the O-ring and O-ring surrounded portion of the spin motor shaft positioned within the axial bore of the holographic disk. The O-ring is axially compressed to radially expand the O-ring thereby eliminating the clearance between the spin motor shaft and the bore of the holographic disk. Thereafter, the holographic disk is secured to the motor shaft with the O-ring remaining in a compressed state.

BACKGROUND OF THE INVENTION 
The present invention relates to holographic disk mounting systems and, 
more particularly, to a method and apparatus for mounting a holographic 
disk on a spin motor shaft which utilizes the radial expansion of an 
axially compressed O-ring to eliminate clearance between the holographic 
disk and spin motor shaft. 
Holographic spinners are used for scanning a laser beam across a surface 
for purposes of writing or reading. The rapidly spinning holographic disk 
imposes a number of constraints upon the designer. The disk must be 
maintained in accurate perpendicular alignment with the axis of rotation 
and must also have zero radial play in order to preserve dynamic balance 
of the assembly. Various holographic disk mounting systems have been 
proposed in the art. For example, U.S. Pat. No. 4,353,615 discloses a 
dynamic mounting system for holographic spinners utilizing a self-aligning 
bearing while U.S. Pat. No. 4,556,278 discloses a free-floating mount for 
a holographic disk. In both patents, the centrifugal force developed by 
rotation of the disk is employed to align the disk with the axis of 
rotation. In each case, the mounting systems are relatively complex and, 
therefore, expensive. 
It is, accordingly, a general object of the present invention to provide an 
improved method and mounting system for holographic disks. 
It is a specific object of the invention to provide a holographic disk 
mounting system and method that provides precise perpendicular alignment 
of the disk to the axis of rotation while achieving zero radial play. 
It is another object of the present invention that the mounting system 
imposes minimum stresses in the holographic disk. 
It is a still further object of the present invention to provide a method 
and apparatus for holographic disk mounting which permits positive, 
repeatable disk alignment. 
It is a feature of the invention that the mounting system utilizes 
inexpensive simple parts to achieve the desired objectives of precise 
perpendicular alignment and zero radial play. 
It is another feature of the invention that the mounting system can be used 
over a wide range of temperatures. 
SUMMARY OF THE INVENTION 
The invention utilizes the radial expansion of an axially compressed O-ring 
positioned in the axial bore of the holographic disk and around the motor 
shaft to eliminate play between the motor shaft and holographic disk. The 
holographic disk is secured to the motor shaft with the compressed O-ring 
remaining in its compressed state.

Turning now to the drawings, a holographic deflector assembly indicated 
generally by the reference numeral 10 comprises a housing 11, a spin motor 
12, a holographic disk 14 having at least one holographic facet, a disk 
mounting assembly 16 (shown in greater detail in FIG. 2), and an optical 
system formed by prism 18 and lens 20. A laser beam 21 is deflected in a 
known manner by the holographic planar disk holographic facet(s) to 
produce a scanning locus for the laser beam that is focused by lens 20 
upon a scanning surface (not shown). 
Referring now to FIG. 2, the holographic disk 14 has a fixed disk center 
bushing 22 which defines a bore 24. The spin motor 12 has a rotating shaft 
25 that includes a threaded bore 26, the purpose of which will be 
described subsequently. Connection of the holographic planar disk 14 to 
the rotating shaft 25 of the spin motor is accomplished by means of an 
intermediate hub assembly 27. The hub assembly 27 comprises an outer 
sleeve 28 press fitted on an inner hub 30 and one or more set screws 32 
that are employed to dynamically balance the rotating elements. Hub 30 
contains a through bore 34, the lower end of the which, as viewed in FIG. 
2, extends through an annular shaft portion 35 that terminates in a 
reduced diameter or shoulder portion 36. The diameter of shaft portion 35 
is slightly less than the diameter of the holographic disk bushing bore 
24. The clearance between hub shaft 35 and the holographic disk bore 24 is 
necessary so that the holographic disk can be fitted onto the shaft 35 and 
seated fully against the hub assembly annular reference surface 37 without 
restraint from the bore 24. The plane of the reference surface 37 is 
normal to the rotational axis of the spin motor shaft 25. This 
relationship can be achieved either by finish machining after attachment 
of the hub assembly to the spin motor shaft or by making the plane of 
reference surface 37 perpendicular to the longitudinal axis of bore 34. 
This arrangement permits the accurate perpendicular registration of the 
holographic disk with respect to the rotational axis. 
A compressible O-ring 38 is positioned around the reduced diameter end 
portion 36 of the hub shaft 35 and then the holographic disk is mounted on 
hub shaft 35 with the planar surface of the holographic disk in contact 
with the planar reference surface 37. A thrust ring 40 having a bore 42 is 
placed against the outer or lower, as viewed in FIG. 2, surface of the 
holographic disk 14 and two Belleville type spring disk washers 44 and 46 
are placed around a cap lock 48 having a bore 50. Screw 52 is then 
inserted through bore 50, the disk spring washers 44 and 46, bore 42 of 
the thrust ring 40 and, finally, through holographic disk bore 24, O-ring 
38, hub bore 34 and into the threaded bore 26 of the motor shaft. 
It will be appreciated that as screw 52 is tightened, springs 44 and 46 are 
compressed forcing the thrust ring 40 against the outer surface of the 
holographic planar disk which in turn seats the disk against the planar 
reference surface 37 of the hub assembly 27. The spring rates of springs 
44 and 46 can be selected to tune the vibrational response of the rotating 
holographic disk assembly and to control the load on the glass of the 
holographic disk. 
Since the axial compression of the O-ring 38 produces the radial expansion 
of the O-ring that eliminates the clearance between the hub shaft 35 and 
the holographic disk bushing bore 24, it will be understood that the 
O-ring cannot take a set. A variety of conventional materials can be 
employed to form the O-ring. One suitable material is nitrile (Buna-N 
(elastomer durometer 65-75 shore A). 
From the preceding discussion of the mounting system and method of the 
present invention, it will be appreciated that the hub assembly 27 and, 
specifically, the shaft 35, reduced diameter end portion 36 and reference 
surface 37, can be formed as a single element and, if desired, as an 
integral part of the motor shaft 25. Alternatively motor shaft 25 and hub 
30 can be formed integrally with a separate sleeve 28 secured to the motor 
shaft 25. 
Other modifications can also be made without departing from the scope of 
the invention as defined in the following claims.