Adjustable photosensor mounting arrangement for a centrifuge

A mounting arrangement for a rotor speed photosensor assembly includes a mounting ring fixedly attached to the stationary element of the centrifuge. The mounting ring has a cutout portion thereon which is adapted to receive a photosensor mounting board which carries the photosensor assembly. Adjustable mounting elements connect the photosensor mounting board to the mounting ring and permit the precise adjustment of the sensor with respect to the ring to thereby dispose the sensor in a predetermined optimal speed-sensing relationship with respect to the rotor.

FIELD OF THE INVENTION 
This invention relates to a mounting arrangement for mounting a photosensor 
assembly used to monitor the rotational speed of a rotor element of a 
centrifuge. 
BACKGROUND OF THE INVENTION 
The rotational speed at which a centrifuge rotor is moving may be monitored 
by the use of a photosensor assembly comprising a phototransmitter, such 
as a light emitting diode (LED), and a photodetector, such as a 
phototransistor. The photosensor assembly is mounted with respect to the 
underside of the rotor element on a mounting ring which is fixed with 
respect to the rotor. The underside of the rotor carries a speed indicia 
in the form of a banded speed decal having alternate radially extended 
contrasting colors thereon. One of the bands of the decal is light 
reflective while the other band is light absorptive. The passage of the 
alternately colored bands past the photosensor assembly results in the 
generation of a pulse train the frequency of which is representative of 
the rotational speed of the rotor. 
The phototransmitter and the photodetector are typically mounted in the 
same housing and must be carefully positioned with respect to the 
undersurface of the rotor. This care is required because the photodetector 
portion of the photosensor assembly is particularly position sensitive. 
That is to say, slight misadjustments in the optimum spacing between the 
underside of the rotor element and the photosensor assembly may result in 
the photodetector losing sensitivity and thereby being unable to 
accurately respond to the radiation reflected from the speed indicia. As 
an example of the care required, it is not uncommon to require accuracy on 
the order of ten thousandths (0.010) of an inch when mounting the 
photosensor assembly. However, because of tolerance variations present in 
the various constituent elements of the centrifuge apparatus, meeting this 
tolerance level requires accuracy in a relatively large number of various 
dimensional adjustments in order to insure the optimal positioning of the 
photosensor assembly with respect to the rotor. Of course, such 
dimensional criticality mandates an extremely costly manufacturing 
procedure, which is perceived to be disadvantageous. 
Accordingly, it is believed to be desirable to provide a mounting 
arrangement for the photosensor assembly to facilitate the mounting and 
adjustment of the position of the photosensor assembly with respect to the 
rotor. 
SUMMARY OF THE INVENTION 
The present invention relates generally to a mounting arrangement for a 
photosensor assembly used to monitor rotor rotational speed. For this 
purpose, the rotor is provided on the undersurface thereof with a speed 
sensing indicia, e.g., a speed decal. The mounting arrangement includes a 
photosensor mounting ring fixedly connectable on the centrifuge stator so 
as to lie within a predetermined range of distances with respect to the 
speed sensing indicia on the undersurface of the rotating element of the 
centrifuge. The photosensor assembly is itself carried on a sensor 
mounting board. The photosensor mounting board includes a ledge sized to 
receive a photosensor assembly therein. The photosensor mounting board is 
connected to the mounting ring through a pair of adjustment elements 
disposed at each end of the mounting board. Manipulation of the adjustment 
elements displaces the photosensor mounting board with respect to the 
mounting ring to thereby cooperably bring the photosensor assembly into a 
predetermined optimal speed-sensing relationship with respect to the 
indicia.

DETAILED DESCRIPTION OF THE INVENTION 
Throughout the following detailed description similar reference numerals 
refer to similar elements in all figures of the drawing. 
With reference to FIG. 1 shown in side elevation is a centrifuge rotor 
generally indicated by reference character 10 having a speed-detecting 
photosensor assembly 12 carried by a photosensor mounting board assembly 
14 adjustably mounted in accordance with the present invention. The 
centrifuge 10 includes a stationary framework, or stator, indicated 
schematically by reference character 18. The stator 18 includes a drive 
housing portion 20 which receives a drive cartridge 22. These elements are 
contained within a vacuum seal assembly housing 24. The drive cartridge 22 
contains a suitable source of rotational energy such as an oil turbine or 
other motive source (not shown). The drive cartridge 22 is covered by a 
top cap 26. The rotational output from the motive source is conducted via 
a shaft 28 to a mounting spud 30. The spud 30 has a spring loaded locking 
detente 34 thereon. An array of teeth 36 is provided on the periphery of 
the spud 30 for use by an alternate, magnetic speed sensing arrangement. 
A rotating element or rotor 38 is removably mounted to the spud 30. The 
undersurface 40 of the rotor 38 is provided with a speed indicia such as a 
decal 42. As shown in FIG. 1A, which is a fragmentary bottom view of the 
rotor 38, the speed decal 42 includes a pattern having alternate radially 
extending bands of a light-reflective and light-absorptive material as 
indicated by reference characters 44 and 46, respectively. 
As seen in connection with FIGS. 1 and 2 the top cap 26 extends upwardly 
from the upper surface of the seal assembly housing 24. The drive shaft 28 
is suitably mounted for rotation on bearings (not shown). The shaft 28 
extends through and above the top cap 26 for a distance sufficient to 
receive the rotor 38 on the spud 30 in a manner which permits rotation of 
the rotor 38 without interference with the centrifuge stator 18. A 
photosensor mounting ring 52 is non-rotationally mounted to the top cap 26 
by a lock washer 54. The attachment of the photosensor assembly 12 and 
mounting board 14 to the ring 52 in accordance with this invention will be 
described in more detail herein. 
A printed circuit board 58 (FIG. 2) of arcuate configuration carrying 
circuit elements for various centrifuge control functions is received by a 
pin connector 60 that is disposed radially adjacent to the exterior of the 
seal assembly housing 24. The connector 60 is connected to the centrifuge 
control network (not shown). A cover 62 having an insulation ring 64 
disposed therebeneath is mounted on projections 66 on the seal assembly 24 
so as to surround the exterior of the same and to support the insulating 
ring 62 over the board 58 and ganged wiring emanating therefrom. These 
members are omitted from FIG. 1 for clarity of illustration. The cover 62 
has an aperture 62A. The photosensor mounting ring 52 projects with an 
annular clearance upwardly through the central aperture 62A. The annular 
clearance between the mounting ring 52 and the cover 62 is closed by a 
heat shield 68 (also not shown in FIG. 1 for clarity of illustration). The 
heat shield 68 carries array of standoffs 68S thereon. The standoffs 68S 
receive threaded screws 69 which extend into the projections 66 to secure 
the entire structure in its assembled relationship. 
The photosensor assembly 12 and the mounting board 14 therefor are believed 
best seen in FIG. 3. The mounting board 14 takes the form of an arcuate 
printed circuit board 70 having mounting apertures 72A and 72B at each end 
thereof. A ledge 74 is provided substantially midway along the inner edge 
of the board 70. The photosensor assembly 12 is mounted on a spacer block 
76. The block 76 is adhesively secured to the ledge 74. The photosensor 
assembly 12 is preferably of the type which includes a phototransmitter 
12T and a photodetector 12D thereon. Suitable for use as a 
phototransmitter and photodetector are the devices made by TRW Optron sold 
under model numbers OPB-706/707. The leads from the sensor assembly 12 are 
soldered to the board 70. These leads are connected by conductors included 
within the ganged wiring 67 which leads to the board 58 and, via the pin 
connector 60, to the centrifuge control. 
As seen in FIGS. 3 through 7, the photosensor mounting ring 52 is a 
substantially annular member having a cylindrical upper portion 52C and a 
conical lower portion 52L that terminates in a lower rim 52R. The ring 52 
has a central aperture 52A therethrough. The aperture 52A is sized to 
accept the top cap 26. The snap lock washer 54 is received on a steel 
washer 77 (FIG. 1) itself received by a shoulder 52S which is provided on 
the ring 52. The washer 54 is accepted by a groove 26G on the outer 
surface of the top cap 26. 
The cylindrical upper portion 52C is undercut, as at 78, for a first axial 
distance (measured relative to the axis of the ring 52) leaving a 
disk-like arcuate plate 52D. The portion 52C is further undercut, as at 
80A and 80B, for a second axial distance to define shoulder surfaces 82S-1 
and 82S-2 that are circumferentially adjacent to (but axially spaced from) 
the undersurface of the disk-like plate 52D (FIG. 6). The cutout region 84 
(FIG. 7) defined between radial surfaces 86A and 86B is angularly 
coextensive with the angular dimension of the mounting board 70. Mounting 
openings 52H-1 and 52H-2 extend through the ring 52 in a direction 
parallel to the axis of the ring 52. A notch 52N is provided in the ring 
52. The notch 52N is sized to closely receive the spacer block 76 which 
carries the photosensor assembly 12. 
As noted earlier the sensitivity of the photodetector 12D is dependent in 
large measure upon the spacing between the speed decal 42 on the 
undersurface 40 of the rotor 38 and the photodetector 12D. Heretofore, it 
is required that precise tolerances be maintained while assembling each of 
the above-described elements during the manufacture of the rotor in order 
to insure that the optimal spacing is defined between these elements. 
However, with the mounting arrangement in accordance with this invention 
the requirement of such precision during assembly of the centrifuge is no 
longer required. 
In accordance with this invention mounting board 70, having the sensor 
assembly 12 secured thereto, is affixed to the ring 52 by first and second 
adjusting elements 90A and 90B, respectively. The first and second 
adjusting elements preferably take the form of threaded screws 92A and 92B 
which extend through the apertures 52H-1 and 52H-2 in the ring and through 
the apertures 72A and 72B in the mounting board 70. The screws 92 are 
secured by corresponding lock nuts 94A and 94B disposed on the 
undersurface of the mounting board 70. The lock nuts 94 (preferably PEM 
nuts) are fixed to the undersurface of the board 70. First and second 
compression springs 96A and 96B are respectively disposed about each of 
the screws 92 to bias the board 70 with respect to the ring 52. Depending 
upon the degree to which the adjusting screws 92 are threaded onto their 
associated lock nuts 94 the clearance dimension 97 (FIG. 7) defined 
between the top surface of the sensor assembly 12 and the upper surface 
52S of the mounting ring 52 may be varied. In this manner the sensor 
assembly 12 may be brought into the optimal distance relationship from the 
rotor 38, thereby optimizing the operation of the photodetector 12D. 
In practice, the setting of the sensor 12 with respect to the undersurface 
40 of the rotor 38 may be understood by reference to FIG. 5. When the 
sensor assembly 12 is initially mounted to the ring 52 and the ring 52 
mounted to the top cap 26, the ring 52 and, therefore, the sensor assembly 
12 mounted thereto, lies within a predetermined range of distances from 
the undersurface 40 of the rotor 38. With the rotor spud 30 secured to the 
shaft 28 a height setting gauge 98 (FIGS. 4 and 5) is disposed over the 
top surface of the spud 30. The gauge 98 includes an extension 99. The 
undersurface 99S of the extension 99 is arranged to lie a predetermined 
distance below the sput 30 at a distance which defines the optimal 
clearance distance between the sensor assembly 12 and the speed decal 42. 
With the gauge 98 thus positioned the adjusting elements 92 are 
manipulated to displace the mounting board 70 with respect to the mounting 
ring 52. In this manner the sensor assembly 12 may be expeditiously, 
repeatably and accurately brought into the predetermined optimal 
relationship with respect to the undersurface 40 of the rotor 38. 
Those skilled in the art having benefit of the teachings as hereinabove set 
forth may effect numerous modifications thereto. These modifications are, 
however, to be construed as lying within the scope of the present 
invention as defined by the appended claims.