Lens focusing mechanism

A lens focusing mechanism 10 including a bracket 18 for retaining a lens 14. The bracket 18 has a bearing 22 attached thereto or integral therewith. The bearing 22 is eccentric relative to the leans 14 and is effective to move the lens 14 along an optical axis 16 thereof. Movement is effectuated by a drive mechanism 34 in a smooth manner and without lubrication. In a specific embodiment, the bearing 22 is eccentric and external to a cylindrical volume defined by the periphery of the lens 14.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to electro-optical systems. More 
specifically, the present invention relates to autofocus apparatus for 
electro-optical systems. 
While the present invention is described herein with reference to 
illustrative embodiments for particular applications, it should be 
understood that the invention is not limited thereto. Those having 
ordinary skill in the art and access to the teachings provided herein will 
recognize additional modifications, applications, and embodiments within 
the scope thereof and additional fields in which the present invention 
would be of significant utility. 
2. Description of the Related Art 
Electro-optical lens systems are currently used in many missiles to provide 
an image which is converted into an electrical signal for display, 
guidance and/or processing. For missile and other guided vehicle 
applications, a highly accurate autofocus system is required to 
automatically focus the lens in response to a control signal. For these 
applications, the required accuracy is on the order of 100 times the 
accuracy of autofocus systems for a typical Browning camera. Hence, the 
tolerances and clearances of conventional autofocus systems for missiles 
are critical. 
The conventional autofocus system for a missile is characterized by the 
movement of the lens within a threaded shaft. Unfortunately, the threaded 
shaft tends to adversely affect the optical train of the system. That is, 
the tolerances of such systems are such that the slight tilting of the 
lens, resulting from the use of the threaded drive, are sufficient to move 
the image off the center of the lens. 
Further, it is often difficult to move the lens in a smooth manner on the 
threaded shaft without substantial lubrication. Yet, the use of a 
lubricant is problematic in that it often dries or dissipates. In 
addition, lubrication must be used with care to avoid contamination of the 
lens. 
Conventional autofocus systems also tend to be electrically and 
mechanically unstable, suffer low yields in fabrication, exhibit latent 
failure modes and tend to be unreliable. 
Thus, there is a need in the art to improve the performance and 
manufacturability of autofocus systems used in missile guidance and other 
demanding applications. 
SUMMARY OF THE INVENTION 
The need in the art is addressed by the autofocus system of the present 
invention which is adapted for use with a lens having a primary optical 
axis extending through the center thereof. The autofocus system of the 
present invention includes a bracket for retaining the lens having a 
bearing attached thereto or integral therewith. The bearing is eccentric 
relative to the lens and is effective to move the lens along the optical 
axis thereof, in a smooth manner, in response to a drive mechanism. While 
lubricants are not required with the design of the present invention, the 
invention allows the use of solid film lubricants, where desired, which 
are less likely to contaminate the optical assembly. In a specific 
embodiment, the bearing is eccentric and external to a cylindrical volume 
defined by the periphery of the lens. 
In more specific embodiments, a linkage is provided between the bearing and 
the drive mechanism. Two embodiments of the linkage are disclosed, a ball 
joint design and a flat blade design.

DESCRIPTION OF THE INVENTION 
Illustrative embodiments and exemplary applications will now be described 
with reference to the accompanying drawings to disclose the advantageous 
teachings of the present invention. 
FIG. 1 is a simplified illustrative sectional side view of a conventional 
autofocus system 10'. The conventional autofocus system 10' includes a 
housing 11'. The housing 11' retains a primary lens 12' and a secondary 
lens 14'. The secondary lens 14' is concentric with the primary lens 12'. 
The primary lens 12' and the secondary lens 14' have a common optical axis 
16'. The secondary lens 14' is mounted within a lens cell consisting of an 
annular bracket 18' which has axial drive screw threads 19' about the 
periphery thereof. The threads 19' engage mating threads within a drive 
motor rotor 20'. The motor rotor 20' is concentric with the lens 14' and a 
drive motor stator 22' which is ordinarily attached to the housing 11. 
When the drive motor is activated, the lens 14' moves back and forth along 
the optical axis 16' thereof as a result of the threaded engagement of the 
bracket 18' with the rotor 20'. Anti-rotation and axial stabilization of 
the lens cell is provided by (3) spring-loaded guide rods 23'. 
FIG. 2 is a perspective rear view of the autofocus system 10 of the present 
invention. FIG. 3 is a simplified illustrative sectional side view of the 
autofocus system 10 of the present invention. The autofocus system 10 
includes a housing 11 which retains a primary lens 12 and a secondary lens 
14. The secondary lens 14 is concentric with the primary lens 12 and has a 
common optical axis 16 therewith. The secondary lens 14 is mounted within 
a lens cell 20 containing an annular bracket 18, an eccentric guide 
bearing 22 which extends from the annular bracket 18, and an anti-rotation 
tang 36. As shown in FIG. 3, lens 14 is circumscribed and supported by 
bracket 18 for joint movement along optical axis 16. 
A particularly unique aspect of the invention is the provision of the guide 
bearing 22 which is eccentric relative to the secondary lens 14 and 
external to a cylindrical volume extending along the optical axis 16 and 
defined by the periphery of the annular bracket 18. 
The guide 22 has a longitudinal axis parallel to the optical axis 16 of the 
lenses 12 and 14 having a longitudinal axis parallel to the optical axis 
16. The guide 22 is adapted to receive a bearing shaft 24. The diametrical 
clearance fit is ideally in the range of 0.0001-0.0003 inch over the shaft 
24 to limit the maximum angular excursion of the lens cell 20. An 
anti-backlash spring 25 is located coaxial with the bearing shaft 24, 
between the guide bearing 22 and the housing 11. The anti-backlash spring 
25 operates through the guide bearing 22 to push the lens cell 20 to the 
rear and removes the axial clearance between the driving thread on the 
shaft 32 and the nut 30. The spring 25 is sized to withstand the inertial 
loads from the cell 20 on its bearing resulting from acceleration loads 
applied through the unit housing. When the motor 34 is operating, it will 
allow the spring 25 to push the lens cell 20 to the rear or it will pull 
it back against the resistance of the spring. Hence, the system 10 is a 
zero backlash system. This facilitates a smooth operation. The 
anti-backlash spring 25 also serves to minimize friction due to off-axis 
loads. 
A solid-film lubricant, such as tungsten disulphide, may be applied to both 
the shaft 24 and the guide bearing 22, although such lubrication should 
not be necessary for most applications. In the preferred embodiment, the 
film thickness is less than 20 millionths of an inch and forms a molecular 
bond with the base materials (no resin binder is used), and when the film 
is properly processed, it does not spall off as dust or migrate to other 
surfaces as a contaminant. Functionally, the guide bearing 22 is canted on 
the shaft 24 because the force of the anti-backlash spring 25 is reacted 
by the offset connection with a drive linkage 28. This leaning of the 
guide bearing 22 on the shaft may be critical to the performance of the 
bearing in some applications. Two crescent-shaped zones may be provided at 
the ends of the guide bearing 22 to make contact with the shaft 24 and 
serve to nestle the guide bearing reliably on the shaft. The straightness 
and cylindricity of the shaft 24 provide the inherent precision of 
straight-line travel required of this device. The guide and shaft contact 
areas must be highly burnished to provide smoothness of motion and low 
friction. The combination of materials should be chosen to become self 
burnishing during run-in cycles at manufacture and remain wear resistant 
within a certain operating life. For example, in the preferred embodiment, 
tungsten di-sulphide was chosen as a lubricant, stainless steel was chosen 
for the shaft 24, and titanium alloy was chosen for the guide bearing 22. 
The nestled position of the guide bearing on the shaft 24 keeps the lens 
cell 20 firmly seated in its aligned position, even during shock and 
vibration. 
A clevis 26 extends from the guide bearing 22 from the bracket 18 above the 
shaft aperture. The H-shaped link 28 is pinned to the clevis 26, 
protruding from the guide bearing 22, at one end and to a drive nut 30 at 
the other. The H shape effectively provides a tightly restrained 
anti-rotation for the threaded nut 30. This assures good servo 
responsivity of the motor to the servo commands and reduces any "hunting" 
characteristic due to looseness. This tightness also requires precise 
machining for the motor seat in the aligned position to prevent binding of 
the linkage in a sidewise direction when assembled. The threaded nut 30 
has provision to engage a cross shaft or pin. The link 28 may be given a 
banana-shaped profile to clear structural elements in the environment. 
As shown in the sectional side view of FIG. 3, the drive nut 30 is in 
threaded engagement with a shaft 32 which extends from a drive motor 34. 
One end of the shaft 32 engages a blind clearance hole in the threaded nut 
30. The other end of the shaft 32 is bonded to the shaft (not shown) of 
the motor 34. The opposite end of the motor shaft 35 protrudes and is 
slotted to permit manual rotation, thereby rotating shaft 32, causing nut 
30 to move toward or away from motor 34. Movement of nut 32 causes similar 
movement of attached link 28, clevis 26 and attached bearing guide 22 
along bearing shaft 24. This, in turn, causes bracket 18 and lens 14 to 
move along primary optical axis 16 facilitate manual positioning of the 
lens 14 to the nominal focus position during optical and electrical 
alignments. The motor 34 is rigidly attached to the housing 11 37 degrees 
off the optical axis due to optical path restraints. Hence, the linkage 28 
and 30 is a two-pin linkage to accommodate the off-axis motor position. 
A tang 36 is diametrically opposed to the clevis 26 on the bracket 18. As 
shown in the rear view of FIG. 4, the tang 36 is retained between two 
eccentric bearings 38. The eccentric bearings 38 are pivotally mounted on 
housing 11 via set screws 40, to allow for the centering of the bracket 18 
(relative to the longitudinal axis 16), and provide for the anti-rotation 
thereof. The dowel pins in this embodiment, used to attach the link 28 to 
the clevis 26 were precision fit. As discussed below, the links of the 
alternative embodiments incorporate a novel and advantageous use of roll 
(spiral) pins for this purpose. Position and temperature sensors may be 
incorporated as is known in the art. (A linear variable transformer-LVDT 
and a thermistor were used in the preferred embodiment as is common in the 
art). 
The unit 10 may be aligned in a conventional manner. During focus 
adjustment, smooth and precise axial translation of the lens cell 20 is 
afforded by activation of the motor 34. When the drive motor 34 is 
activated, the threaded shaft 32 rotates and moves the drive nut 30. The 
drive nut 30, in turn, moves the H-link 28. Movement of the H-link 28 is 
transferred to the lens cell 20 via the clevis 26 on the guide 22 of the 
lens cell 20. 
FIG. 5 shows a side view of a first alternative embodiment of the linkage 
for the autofocus system 10 of the present invention in which the H-shaped 
link is replaced with a ball-joint link. The ball-joint accommodates 
angular misalignments in two directions and serves the primary function of 
connecting the sliding bearing with the lens cell 20. The ball-joint link 
50 includes a housing 52 which accommodates a threaded, split, C-shaped 
bushing nut 54 in a spherical seat therewithin, and a threaded rod end 
bearing 56 having an eye bolt 58 at one end thereof. The housing 52 has a 
U-shaped cross section through the longitudinal axis thereof. 
FIG. 6(a) is a top view of the ball-joint linkage 50 of the alternative 
embodiment of the autofocus system of the present invention. FIG. 6(b) is 
a sectional top view of the ball-joint linkage 50 of the alternative 
embodiment of the autofocus system of the present invention. And FIG. 6(c) 
is an view of the ball-joint linkage 50 of the alternative embodiment of 
the autofocus system of the present invention. 
The seating of the C-nut 54 in the seat 55 of the housing 52 is illustrated 
in phantom in the sectional top view of FIG. 6(b). In the preferred 
embodiment, the C-nut 54 is constructed of nylon and has a threaded 
aperture to receive a threaded brass shaft from the motor 34. The 
clearance fit of the C-nut around the motor shaft 32 and the clearance fit 
of the C-nut within the seat 55 are controlled by a nut and washer 
arrangement 60 at the top of the housing 52. See FIG. 6(c). The washer 
arrangement 60 includes a blade 62 which engages the slot in the C-nut 54 
and provides anti-rotation for limiting the angular excursion of the split 
C-shaped nut about a longitudinal axis of the motor 34. A threaded screw 
64 extends through a first stainless steel shim washer 66, one side of the 
housing 52, a washer 68, the blade 62, and a second shim washer 69 into 
engagement with threads in the second side of the housing 52. Thus, by 
tightening the screw 64 and/or removing shims from the washers 66 and 69, 
the clearances in and around the C-nut 54 may be adjusted. The housing 52 
basically acts as a C-clamp around the C-nut. The housing 52 squeezes the 
C-nut 54 until its thread firmly contacts a thread gage. The adjustment is 
then secured in this position. This adjustment not only eliminates the 
clearance resulting from thread tolerances, but provides firm contact and 
improved stiffness of the linkage without a detrimental increase in 
friction in the autofocus assembly. The adjustment achieves low clearance 
values without requiring extremely tight tolerances on the detail parts. 
Returning to FIG. 6(a) an anti-rotation arrangement is provided by a first 
pin 72, which extends from the motor housing in parallel with the motor 
shaft or pin 32, a second pin 74 which extends from the housing 52 
transverse to the first pin 72, and a nylon slider block 76 which links 
the first and second pins 72 and 74 together. FIGS. 6(d) and (e) show 
front and side views of the slider block 76, respectively. The slider 
block 76 moves freely during focus adjustment and is self retaining on the 
pins 72 and 74. 
Returning again to FIG. 6(a), the link housing 52 is threaded at its distal 
end, relative to the motor end, to receive the threaded end of the rod 56. 
This affords precise adjustment of the axial clearance at time of 
assembly. Ordinarily, the threaded rod end is cemented in place once this 
adjustment is made. 
The distal end of the rod 56 includes the eye bolt 58. The eye bolt 58 
includes a ball 59 within a socket in the rod 56. The eye bolt 58 is dowel 
pinned to the clevis 26 of the cell 14 using a tightly wound spiral pin 
80. As is known in the art, spirol pins, manufactured by Spirol 
International Co., are designed to fit snugly into a loosely toleranced 
hole such as a roughly drilled hole. When installed into a hole smaller 
than the pin, the spirally wrapped pin adapts to the size, and within 
limits, to the shape of the hole. This feature is used effectively in this 
design to allow the pin 80 to tightly fit into the outer two holes of the 
U-shaped clevis 26 while only snugly fitting the inner hole of the eye 
bolt 58. The bolt hole is slightly larger than the in-line holes of the 
clevis 26. When installed, the center part of the pin 80 becomes 
barrel-shaped to engage the larger diameter of the eye bolt 58. This 
fitting is controlled by both the tolerances of the parts, and by the 
assembler rotating (winding) the spiral after the pin is in place to 
attain the desired fit. 
In the preferred embodiment, the ball 59 of the rod end 58 is constructed 
of hardened steel while the rod 56 is constructed of medium hard steel. 
The housing 52 and the anti-rotation blade 62 are constructed of aluminum 
alloy, the C-nut 54 is constructed of nylon, and the pins 72 and 74 are 
constructed of stainless steel. Those skilled in the art will appreciate 
that other materials my be used without departing from the scope of the 
invention. 
The operation of the first alternative (ball-joint) embodiment is 
essentially the same as that of the illustrative (H-link) embodiment. 
Activation of the motor 34 causes the C-nut 54 to move on the threaded pin 
32 and exert a force on the housing 52 via the seat 55. Movement of the 
housing 52 translates to axial movement of the lens cell 20 via the guide 
bearing 22 and the rod end 58. 
The use of two spherical bushings, i.e., the C-nut 54 and the rod end 58, 
allows both angular and displacement misalignments to occur in the 
autofocus assembly without producing binding or an increase in friction in 
the linkage. The line-of-action of the ball-joint linkage 50 places the 
two centers of rotation where they produce a very smooth action in 
translating the lens cell 20. The C-nut 54 contains its swiveling center 
directly on the center of the motor axis. The rod end bearing 58 contains 
its swiveling center directly on the center of the pivot pin in the clevis 
26 of the lens cell 20. This arrangement eliminates the eccentricities of 
action found in a two-pin and separate threaded nut linkage system, and 
produces a much smoother action. 
FIG. 7 is a side view of a second (flat blade) alternative embodiment of 
the linkage for the autofocus system 10 of the present invention. FIG. 8 
is a rear view of the flat blade linkage for the autofocus system 10 of 
the present invention. The flat-blade embodiment offers reduced cost 
relative to the ball-joint linkage and improved performance relative to 
the H-link. The flat blade linkage 90 includes a nut 92 and the flat blade 
link 94. The nut 92 threadably engages a shaft extending from the motor 
34. The distal end of the nut 92 includes a clevis 96. The clevis 96 of 
the nut 92 engages the proximal end of the flat blade link 94. The distal 
end of the flat blade link 94 is connected to the clevis 26 of the lens 
cell 20 via a spiral pin 98. 
Thus, the present invention has been described herein with reference to a 
particular embodiment for a particular application. Those having ordinary 
skill in the art and access to the present teachings will recognize 
additional modifications applications and embodiments within the scope 
thereof. For example, as is evident above, the invention is not limited to 
the implementation of the link or the drive motor. The invention is not 
limited to the particular implementation of the guide bearing. Nor is the 
invention limited to the construction or application illustrated herein. 
It is therefore intended by the appended claims to cover any and all such 
applications, modifications and embodiments within the scope of the 
present invention. 
Accordingly,