Thermal compensator assembly

A thermal compensator assembly employed in an optical system to adjust the relative location of lens elements and maintain a preset focus as the ambient temperature changes. The assembly includes a plurality of high linear coefficient of expansion push rods interconnected with levers having relatively low linear coefficients of expansion. The assembly changes in length in direct response to ambient temperature changes. A second lens barrel carrying the objective lens is bias mounted for floating movement with respect to the first lens barrel so as to abut the assembly. The compensator assembly is exemplified as being pin mounted on a first relatively fixed lens barrel. The assembly expands and contracts as a function of ambient temperature to effect movement of the floating lens barrel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
The present invention relates to a mechanical assembly which provides 
linear movement in response to temperature changes. More specifically, the 
present invention relates to improvements in thermal compensator 
mechanisms as employed in optical systems. 
2. Description of the Prior Art: 
The problem of focus distortion in optical systems due to changes in 
temperature has been frequently discussed in the prior art. Generally, 
temperature variations cause glass lenses to expand or contract and 
therefore vary the indices thereof. The lens mounts also tend to expand or 
contract due to changes in temperature and additionally affect the focal 
point. In order to maintain a fixed focal point throughout wide variations 
in temperature, many systems have been developed for compensating the 
above mentioned expansion and contraction. 
In U.S. Pat. No. 1,325,936, compensation was achieved between two lenses by 
mounting each lens in separate mounting barrels and connecting the barrels 
at a point removed from the lenses. The two barrels were made of materials 
having different thermal coefficients of expansion, so that any change in 
temperature resulted in a separation change between the lenses 
corresponding to the difference between the two barrel expansions or 
contractions. 
In U.S. Pat. No. 2,533,478, compensation was achieved by mounting the 
lenses in a barrel having a relatively low thermal coefficient of 
expansion and connecting one end of the lens barrel to an expandable 
sleeve having a relatively high thermal coefficient of expansion. The 
other end of the expandable sleeve was connected to an outer support 
sleeve having a relatively low thermal coefficient of expansion. 
In U.S. Pat. No. 2,537,900, compensation was achieved by mounting the 
lenses in a barrel having a relatively low thermal coefficient of 
expansion and connecting one end of the lens barrel to a camera body. The 
camera body had a relatively high thermal coefficient of expansion to vary 
the position of the focal point in compensating fashion to maintain the 
preset focus. 
My parent copending U.S. patent application Ser. No. 856,699, cited above, 
employs a linearly expanding and contracting compensator linkage 
constructed of elongated link elements having alternately dissimilar 
linear coefficients of expansion. The link elements are adjacently 
arranged in link pairs and the links in each pair are joined at a first 
end so to appear folded. Each link pair includes a first link element 
having a relatively high linear coefficient of expansion and a second link 
element having a relatively low linear coefficient of expansion so that 
the resultant movement of one end of the link pair is due to the 
difference between coefficients of expansion and the amount of movement of 
each preceding link member. 
My related copending U.S. patent application Ser. No. 860,345, cited above, 
employs a serpentine channel having several elongated channel portions 
running parallel to the optic axis. The serpentine channel is formed in a 
relatively fixed lens barrel having a relatively high linear coefficient 
of expansion. A floating lens barrel is thermally compensated by a series 
of balls having a relatively low linear coefficient of expansion located 
in the serpentine channel. When the serpentine channel linearly expands 
with the expanding fixed lens barrel, the balls relocate along the channel 
due to biasing of the floating lens barrel in contact with the balls. 
SUMMARY OF THE INVENTION 
The present invention overcomes the basic size restriction problem inherent 
in the prior art, as well as offering an alternative to the compensator 
linkage disclosed and claimed in my aforementioned earlier filed 
applications. 
Large compensational adjustments are obtainable with the present invention 
to account for changes in the ambient temperature and the resultant 
changes in the optical system. A unique linkage is employed for amplifying 
the predicted temperature length changes occuring in individual link 
elements and adjusting the relative distance between a lens element in a 
floating lens holding barrel and the lenses in a first relatively fixed 
barrel by an amount sufficient to maintain a preset system focus. 
Amplification is achieved in each link by an expandable push rod connected 
between a reference and a pivoted lever mounted on the outer surface of 
the first lens barrel. The expandable push rod abuts a point on the 
pivoted lever to effect a mechanical advantage between the expansion 
movement of the push rod and the movement of the other end of the pivoted 
lever, resulting in the push rod movement being amplified. A series of 
links, wherein a push rod of each link abuts the movable end of the lever 
of the immediately preceding link and the intermediate point of its 
associated lever, are serially arranged in order to multiply the 
mechanical advantage of each individual link and effect a relatively large 
compensational adjustment of the floating lens barrel with a relatively 
short linkage assembly. 
It is an object of the present invention to provide a lightweight thermal 
compensator assembly. 
It is another object of the present invention to provide a compact thermal 
compensator assembly suitable for use in optical systems. 
It is a further object of the present invention to provide a thermal 
compensator assembly which employs a mechanical amplification technique to 
provide compensational movement of a lens element to maintain a preset 
focus as ambient temperature changes.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The embodiment of the present invention is shown in FIGS. 1 and 2, employed 
in an optical lens system. A first relatively fixed lens holding barrel 10 
is shown as being concentric within an outer, relatively movable objective 
lens holding barrel 12. Generally, the first lens holding barrel 10 is 
rigidly mounted to a support mechanism of a telescope or other optical 
device and is constructed of a lightweight material having a relatively 
high linear coefficient of expansion, such as aluminum or magnesium. 
The outer lens holding barrel 12 contains a lens element 18 and is 
supported for movement with respect to the first lens holding barrel 10 by 
a plurality of ball bearing assemblies. Each ball bearing assembly 
includes a groove 14 which extends linearly along the outer surface of the 
lens barrel 10 parallel to an optical axis 11. Corresponding grooves 15 on 
the inner surface of the outer barrel 12 provide bearing surfaces for 
roller bearings 16 mounted therein. 
The thermal compensator assembly is mounted for independent movement on 
lens barrel 10 so as not to be influenced by thermal expansion in the lens 
barrel 10. An elongated support member 30 having a relatively low linear 
coefficient of expansion, such as Kovar or Invar, is connected to the lens 
barrel 10 by a pin 31. The lens barrel 10 contains a linear groove 35 
which extends longitudinally therein in a direction parallel to the optic 
axis 11. A pin 33 extends from the elongated support member 30 into the 
groove 35. Therefore, when the lens barrel 10 either expands or contracts 
longitudinally, such movement does not effect the support member 30. 
A first push rod 42 having a relatively high linear coefficient of 
expansion, such as aluminum, is mounted on the elongated support member 30 
in a socket 32. The push rod 42 is mounted so as to expand and contract 
linearly along a line parallel to the optic axis 11. A first lever element 
45 having a relatively low linear coefficient of expansion, such as Kovar 
or Invar, is pivotally mounted at a first end 34 to the elongated support 
member 30 and abutted by a second end 44 of the first push rod 42. 
Expansion of the push rod 42 causes the second end 47 of lever 45 to move 
in a direction generally parallel to the optic axis. It is understood that 
the second end 47 moves in an arc segment; however, due to the rather 
limited distance involved, that movement is considered to be generally 
parallel to the optic axis 11. In the preferred embodiment, the second end 
44 of the first push rod 42 abuts an intermediate point on the first lever 
45 to provide a mechanical advantage of 3:1. This abutment is maintained 
by a biasing compression force on the assembly and a small socket at the 
intermediate point that mates with the push rod. Such location means that 
the second end 47 of the lever 45 moves a distance which is three times 
greater than the excursion of the second end 44 of the push rod 42. The 
first push rod 42, in combination with the first lever 45, forms a first 
link in the assembly linkage. That link could be serially combined with 
similar links to provide a desired amount of movement of the floating lens 
barrel 12 in response to ambient temperature changes. The embodiment of 
FIGS. 1 and 2 is shown to include a series of links. 
A second link comprises a second push rod 46 and a second lever 49 between 
the first link and a third link. The second push rod 46 abuts between the 
second end 47 of the first lever and an intermediate point 48 on the 
second lever 49. The first end of the second lever 49 is connected to the 
support member 30 by a pin 36 for pivotal rotation. A third link is shown 
including a third push rod 50, which abuts between the second end 51 of 
the second lever 49 and an intermediate point 52 on its associated third 
lever 53. 
A fourth push rod 54 is shown abutting between the second end 55 of the 
third lever 53 and a tab 61 which extends radially from inside the lens 
barrel 12. 
A biasing spring 20 is connected between a post 22 extending from the 
floating lens barrel 12 and a pin 24 extending from the lens barrel 10. 
The biasing spring 20 tends to hold the lens barrel 12 against the optical 
compensator assembly and retract the lever movements when the push rods 
contract due to lowering the ambient temperature. 
Second and third compensator assemblies are shown evenly placed around the 
lens barrel 10. Elements of those assemblies are identical to those shown 
in the first optical compensator described above and identical shown 
elements have character numerals respectively prefaced with "1" and "2". 
The combination of three optical compensators shown in FIGS. 1 and 2 
therefore provide balanced pressures to effect a smooth and continuous 
movement of the lens barrel 12 when such compensation is necessary. 
As mentioned above, the disclosed embodiment employs linkages which each 
exhibit a 3:1 mechanical advantage with respect to the amount of linear 
excursion of the associated push rod. Based upon that known mechanical 
advantage, the amount of total excursion is predicted, since it is related 
to the number of links in the linkage and the amount of excursion 
contributed by each link. For example, where an assembly includes "n" push 
rods (where n is an integer greater than or equal to 1) and "n-1" levers, 
each link, such as that assembly shown in FIGS. 1 and 2, amplifies its 
associated push rod excursion by a factor of 3, the total excursion is: 
EQU .DELTA.d=3.sup.n-1 d.sub.1 +3.sup.n-2 d.sub.2 +3.sup.n-3 d.sub.3 +3.sup.n-4 
.DELTA.d.sub.4 +. . . +3.sup.n-n .DELTA.d.sub.n 
It can therefore been seen from the above relationship that the first link 
formed by a push rod 42 and lever 45 combine to move the second end 47 of 
the lever 45 by an amount equal to three times .DELTA.d.sub.1, where 
.DELTA.d.sub.1 is the amount of excursion attributed to push rod 42. 
However, with three links and one additional push rod, the total excursion 
would be; 
EQU .DELTA.d=27.DELTA.d.sub.1 +9.DELTA.d.sub.2 +3.DELTA.d.sub.3 
+.DELTA.d.sub.4, 
where .DELTA.d.sub.4 indicates the amount of unamplified excursion 
contributed by the thermal expansion in push rod 54. 
In the event that it is desirable to move the floating lens barrel 12 in a 
direction opposite to the thermal expansion of the lens barrel 10, it is 
readily apparent that the linkage and biasing may be reversed in order to 
effect such movement. Furthermore, it is apparent that the assemblies may 
be mounted on a focusing mechanism which controls selectable movement of 
the objective, rather than the first lens barrel, as shown. 
In addition to the above described embodiment, it will be apparent that 
many modifications and variations may be effected without department from 
the scope of the novel concept of this invention. Therefore, it is 
intended by the apended claims to cover all such modifications and 
variations which fall within the true spirit and scope of the invention.