Laser path seal

A rolling diaphragm seal is inserted between a pair of telescopic tubes containing a laser beam and a reflective mirror to preclude ambient air or lubricant from impinging on the mirror or for changing the density of the air within the tube to cause a change in intensity of the laser beam. The telescoping tube pairs can be used as part of a control system for the positioning of the beds of an ultra-precise machining apparatus such as found in turning and grinding machines for generating flat, spheric, and aspheric shapes, commonly known as aspheric generators. The rolling diaphragm seal consists of a rubber tube having its ends folded back upon itself and positioned between the inner and outer telescoping tubes of each pair. The ends of the seal tube are held apart in a retaining collar through which air can be inserted to pneumatically pressure the space between the folded back portions of the seal.

BACKGROUND OF THE INVENTION 
1. Field Of The Invention 
This invention relates to a seal to assure an air tight laser optical path, 
and more particularly, a rolling diaphragm type seal used in connection 
with a laser control for an aspheric generator. 
2. Description Of The Prior Art 
An aspheric generator, such as that manufactured by the Moore Special Tool 
Co., Inc. of Bridgeport, Conn., is a three-axes computer numerically 
controlled precision maching apparatus designed to produce microinch 
finishes on a broad spectrum of materials. The apparatus can be used for 
single point diamond turning or for grinding. This dual capability allows 
a machinist to not only produce mirror quality finishes, but also to grind 
molds to crucial tolerances for optical lenses, and to handle other 
grinding tasks related to precision machining. In its diamond turning 
mode, the state of the art aspheric generator can produce finished optics 
on the machine and can be used for the production of discs used in the 
computer and photocopier fields. In its grinding mode, the aspheric 
generator can grind to tolerances of twenty millions of an inch (0.5.mu.m) 
or better. This enables it to produce glass optical elements--spheres and 
aspheres--in most cases ready to polish, and ceramics for use as injection 
molding dyes which are used to produce plastic lenses. 
High precision tolerances and resolution are achieved by the use of a laser 
feedback system to control the movement of the beds of the aspheric 
generator apparatus along the various axes, such as the X and Z linear 
axes of the apparatus. The laser feedback system is operated by a suitable 
computer program which outlines the work to be performed on the work piece 
held in the chuck of the machine. 
The laser beams which control movement of the beds of the apparatus, which 
in turn produce the required movement of the tool against the work piece, 
which movement can be measured in microinches to produce the high quality 
finishes which are required, are generated and enclosed in telescoping 
tubes which also house a reflective mirror, an interferometer and a 
receiver to monitor the displacement; and through a comparison 
interferometer network, to cause movement of one of the two tubes provided 
on a linear axis, such as the X or Z axis to achieve the required motion 
of the bed and tool along that axis. The tubes are connected to the 
appropriate tool bed axis to develop the required movement. 
The laser optical path in the laser feedback system tubes must be airtight. 
The humidity within the tubes must be controlled and lubricants must be 
precluded from impinging on the various mirror or interferometer surfaces 
within the tubes. In the former instance, a change in the density of the 
atmosphere within the tubes will effect the intensity of the laser beam 
and its reflective quality causing error in the movement of the tool. In 
the latter instance, if dirt or grease impinge upon any of the mirror 
surfaces, the apparatus must be cleaned and taken apart, resulting in 
considerable down time. Accordingly, a suitable seal between the 
telescoping tubes and the ambient environment must be maintained to 
preclude lubricant and dirt from entering the interior of the tubes and 
the density of the atmosphere within the tubes from being changed during 
operation of the apparatus. 
Heretofore it has been common to use rolling diaphragm seals between 
telescoping parts, such as a piston and cylinder. As disclosed in the June 
19, 1969 issue of "Machine Designing", as a piston moves in a cylinder, a 
rubber seal or sleeve connected between the cylinder and the piston will 
roll off the piston side wall onto the cylinder side wall. This 
effectively seals the space in the cylinder above the piston. The 
diaphragm consists of a single wall sleeve or tube having one end fixed to 
the cylinder and the end fixed to the piston and as indicated, rolls 
between the two elements as the piston travels linearly in the cylinder. 
However, where the length of travel of the telescoping parts is 
considerable, the ends of such a seal tend to frictionally roll against 
each other during the linear travel of the parts creating considerable 
drag or friction and resistance to movement. Where accuracy of movement in 
the millions of an inch category are required, as for example in an 
aspheric generator, such seals cannot be used because of the tendency of 
the material to drag against itself at its ends thereby impeding accurate 
movement. The same would be true of 0-ring seals and bellow-type seals, 
the latter being impeded by undue air friction in its expansion and 
contraction. 
Accordingly, it is the primary object to this invention to provide an 
effective seal between a pair of telescoping tubes housing various laser 
components of a laser feedback system for an aspheric generator. 
It is a further object of this invention to provide a seal of the type 
indicated which provides minimal frictional impedence of resistance to 
movement of the telescoping tubes housing the laser feedback components. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a rolling diaphragm seal is inserted 
between a pair of telescopic tubes containing a laser beam and a 
reflective mirror to preclude ambient air or lubricant from impinging on 
the mirror or for changing the density of the air within the tube to cause 
a change in intensity of the laser beam. The telescoping tube pairs are 
connected to the slides which are a part of a control system for the 
positioning of the beds of an ultra-precise machining apparatus such as 
found in turning and grinding machines for generating flat, spheric, and 
aspheric shapes, commonly known as aspheric generators, by connecting a 
tube pair to the X and Z axis of the generator, respectively, and 
generating electrical signals to precisely position each tube pair and the 
bed along each axis in response to a change in displacement pulses 
generated from the laser beam. 
The rolling diaphragm seal consists of a rubber tube having its ends folded 
back upon itself and positioned between the inner and outer telescoping 
tubes of each tube pair connected to the machine bed. The ends of the seal 
tube are held apart in a retaining collar through which air can be 
inserted to pneumatically pressure the space between the folded back 
portions of the seal. As the telescoping tubes of each pair move relative 
to the other, the spaced portions of the diaphragm seal will roll along 
the interior surface of the outer laser tube and exterior surface of the 
inner laser tube to form a rolling diaphragm seal with a minimum of 
friction between adjacent portions thereof due to the pneumatic spacing of 
the adjacent portions of the seal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in detail, wherein like numerals indicate 
like elements throughout the several views, an aspheric generator is 
indicated generally by the numeral 10 and in phantom in FIG. 1. 
The aspheric generator 10 includes a bed 12 on which a tool can be mounted 
for grinding or turning a work piece held on a vacuum chuck 14. Movement 
of the bed 12 is adapted to be controlled along the "Z" axis 16 and "X" 
axis 18 of the apparatus although it would be understood that additional 
axes of the machine can be controlled such as the "B" rotational axis 20 
and/or the "Y" axis lying in a plane perpendicular to the "Z" and "X" 
axes. 
Movement of the bed 12 is controlled by a laser feedback system generally 
indicated by the numeral 22, which in turn is adapted to receive signals 
from a computer provided with a suitable program for directing movement of 
the bed 12. Generally, the laser feedback system is housed within three 
pair of telescoping tubes generally designated by the numerals 24, 26 and 
28. Each pair of tubes 24, 26 and 28 includes a first inner tube 30 and a 
second telescoping outer tube 32. The smaller diameter inner tube 30 
houses a reflector or mirror 34. The remaining components of the feedback 
system and optical system are isolated and housed within a sealed box 36. 
The relative movement of the telescoping tube pairs 26 control movement of 
the bed 12 along the "X" axis of the apparatus 10 while two tube pairs 24, 
28 control movement of the bed 12 and hence a tool along the "Z" axis of 
the apparatus. 
A laser transducer 38 housed within sealed box 36 generates a given 
intensity laser beam 40 in response to a signal from a computer. The beam 
40 is bent by a bender 42, and split by splitters 44 and 46 and fed 
through benders 48, 50 and 52. The benders 48 and 50 transmit the beam 40 
to a second pair of benders 54 and 56, respectively, which also bend the 
beam 90.degree.. The beam fed by bender 52 through tube pair 24 is bent by 
a bender 58 in a housing 60 and impinges upon a reflector or mirror 34 
within tube pair 26, and is reflected back to an X-axis interferometer 62 
within housing 60. The signal generated by interferometer 62 is 
transmitted to a receiver 64 within sealed box 36. The laser beam 
transmitted by bender 54 impinges upon a mirror 34 within tube pair 28. 
Mirror 34 within tube pair 28 reflects the beam to a Z-axis interferometer 
66 which in turn feeds a signal to a receiver 68 within sealed box 36. The 
laser beam transmitted from bender 56 is fed to a Farrand compensator 70 
where it can be compared with the reflected beams received by receiver 64 
and 68 to cause movement of bed 12 by the use of appropriate drives and 
motors to precisely control the movement of a tool mounted on bed 12. 
In order to preclude the density of the ambient air within each tube pair 
24, 26 and 28 from changing and to preclude lubricant or dirt from 
impinging on the mirrors within the tube pairs, which can effect operation 
of the laser feedback system and thereby the precise control of movement 
of the tool against the work piece, a rolling diaphragm seal generally 
designated by the numeral 80 is provided between each outer tube 32 and 
inner tube 30 of each tube pair 24, 26 and 28 of the laser feedback system 
22. 
Seal 80 includes a flexible rubber tube 82 having its ends folded back on 
itself to provide a pair of spaced annular ends 84 and 86 defining a 
chamber 88 therebetween. The spaced ends 84 and 86 are fastened to a 
suitable split clamp collar 90 provided on outer tube 30 of each pair of 
laser tubes 24, 26 and 28. The collar 90 includes an opening 92 through 
which air can be fed into the annular chamber 88 between the spaced 
portions of the flexible tubular seal 80 to inflate the same with a 
pressure of approximately 0.25 psi to maintain portions of the seal spaced 
from each other along its entire length to preclude one portion from 
collapsing and frictionally rubbing against the other. 
A portion of the diaphragm 82 downstream from collar 90 is anchored by a 
clamp ring 94 to the outer surface of the inner tube 30 and a mirror 
housing 95. An O-ring is disposed between the outer surface of mirror 
housing 95 and clamp ring 94 to maintain minimum contact of the flexible 
diaphragm seal 82 with the outer surface of mirror housing 95. 
In operation, the seal 82 effectively blocks the space between inner tube 
30 and outer tube 32 of each laser tube pair 24, 26 and 28 from the 
ambient atmosphere and the introduction of lubricant, dirt or other 
foreign materials into the interior of either of the tubes through the 
space therebetween. By virtue of the introduction of pneumatic fluid 
between the spaced ends 84 and 86 of the seal 82 into chamber 88, 
frictional contact between a spaced portions of the seal is held to a 
minimum precluding undue drag on the precise movements of the telescoping 
tubes relative to each other. The spaced portions of the diaphragm-type 
seal 82 will roll off the wall of the outer tube 32 and onto wall of the 
inner tube 30 (and mirror housing 95) and vice-versa as the tubes move 
relative to each other, to maintain the seal between the tubes.