Machining a cooled cylindrical optic to compensate for pressure distortion

United States Patent [19]

Eitel

[n] Patent Number: 4,553,457 [45] Date of Patent: Nov. 19, 1985

[54] MACHINING A COOLED CYLINDRICAL OPTIC TO COMPENSATE FOR PRESSURE DISTORTION

[75] Inventor: Frederick G. Eitel, North Palm Beach, Fla.

[73] Assignee: The United States of America as

represented by the Secretary of the Air Force, Washington, D.C.

[21] Appl. No.: 505,166

[22] Filed: Jun. 17, 1983

[51] Int. CI.4 B23B 1/00; B23B 5/00

[52] U.S. CI 82/1 C; 82/2 B;

51/284 R

[58] Field of Search 82/1 R, 1 C, 2 B;

350/310, 320, 295; 51/284 R, 216 LP

[56] References Cited

U.S. PATENT DOCUMENTS

1,494,134 5/1924 Ritterrath .

1,530,441 3/1925 Thomson 350/310

2,851,916 9/1958 Grandy et al 82/1 C

3,210,894 10/1965 Bentley et al 51/284 R

3,521,943 7/1970 Kelderman 350/295

3,596,125 7/1971 Seigel 313/22

3,686,940 8/1972 Kockott 73/150

3,720,120 3/1973 Cutler 82/2 B

3,914,010 10/1975 Zeller 350/3

4,190,327 2/1980 Hughes 350/310

FOREIGN PATENT DOCUMENTS

161180 12/1970 Japan 82/1 C

80240 7/1978 Japan 51/284 R

598698 3/1978 U.S.S.R 82/1 C

OTHER PUBLICATIONS

"Diamond Turning of F-lll Windscreens", Optical Engineering, vol. 17, No. 6, Nov.-Dec. 1978.

Primary Examiner—Leonidas Vlachos

Assistant Examiner—Jerry Kearns

Attorney, Agent, or Firm—Donald J. Singer; Jacob N.

Erlich

[57] ABSTRACT

A system for, and a method of, replicating the known (i.e., ascertained) operational coolant fluid flow local pressure in an optical surface (such as a mirror surface) of the heat exchanger portion of a fluid cooled cylindrical optic. The system essentially comprises a precision numerically controlled lathe having a selectively rotatable spindle on which is mounted, with a hollow adapter, the cylindrical optic in which is retained a fluid connector that is in communication with the adapter which, in turn, is in communication with a source of pressurized fluid containing a fluid whose rate of flow and pressure can be regulated. The pressurized fluid flows serially into the adapter, the connector, and the cylindrical optic and its optical surface, thereby replicating the operational fluid flow pressure through the entire optical surface, without the prior art problem of pressure drops in and pressure deflection of the optical surface which, in turn caused residual finish figure machining error in the optical surface. As a result of the use of this system, and of the performance of the steps comprising the method of replicating the operational fluid flow pressure in the entire optical surface, this prior art residual finish figure machining error is eliminated or at least is significantly minimized.

8 Claims, 4 Drawing Figures

4,553,

1

MACHINING A COOLED CYLINDRICAL OPTIC
TO COMPENSATE FOR PRESSURE DISTORTION

STATEMENT OF GOVERNMENT INTEREST 5

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

BACKGROUND OF THE INVENTION 10

This invention relates generally to optics and more particularly to a system for and a method of replicating the known operational coolant fluid flow local pressure in an optical surface (such as a mirror surface) of a heat exchanger portion of a fluid cooled cylindrical optic to 15 compensate for (and thereby eliminate or significantly reduce) any residual finish figure machining error of the optical surface, which said machining error is normally caused by the coolant fluid flow differential pressure deflection of the optical surface. 20

The technique presently used in an attempt to minimize the abovementioned figuring error involves filling the optic with water, attaching valved plugs to the coolant ports, and subsequently introducing a predetermined static pressure for figuring, i.e., finish figure or 25 contour machining. Generally, the pressure used is predicted coolant average pressure, i.e.,

inlet pressure - discharge pressure + diseharge pressure ^

Since pressure loss in the passages in the optical surface of the heat exchanger portion of the cylindrical optic is usually the largest contributor to the difference between inlet and outlet pressures, it is apparent that 35 large differences can exist between the operating (i.e., operational) pressure and the figuring (i.e., finish figuring machining) pressure. Typically, this results in optical figure error exhibiting a tilt across the heat exchanger for radial and involute passages, and as a local 40 ripple due to the heat exchanger passage geometry, as will be shown later. Additionally, a local bulge or depression is exhibited where manifolds are located within the optical envelope.

One obvious solution to the pressure distortion prob- 45 lem is to duplicate actual coolant flow conditions during figuring. However, a number of problems make this undesirable. Either a very large "blowdown" coolant supply system or a recirculating pumped system is required. The latter would require a temperature control 50 system to maintain coolant temperature. Coolant flow can introduce vibratory pressure fluctuations which can jitter the mirror during figuring. This, in turn, would introduce additional optical figure errors.

Accordingly, what is needed in the art, and is not 55 presently available, is the capability to eliminate (or, at least, to significantly reduce) any residual finish figure machining error of the optical surface of the heat exchanger portion of the cylindrical optic, wherein the aforesaid residual error is caused by coolant fluid flow 60 differential pressure deflection of the optical surface.

SUMMARY OF THE INVENTION

The instant invention satisfies the above-mentioned need in the art. It, therefore, constitutes a significant 65 advance in the state-of-the-art.

According to the invention, the aforementioned need is satisfied by replicating the known (i.e., ascertained)

457

2

operational coolant fluid flow local pressure in the optical surface of the heat exchanger portion of the cylindrical optic during finish figure machining of the optical surface, i.e., by making pressure conditions in the optical surface during finish figure or contour machining approach the operational (i.e., flowing) conditions. Thereby, pressure deflection (and the resultant induced optical distortion) in the optical surface, which is caused by differences in pressure (i.e., pressure drops) in the optical surface, is eliminated or at least is significantly reduced. As a related matter, it is here to be noted: that the cylindrical optic has fluid flow ports and passageways therein, with some of the passageways being located adjacent to and internal of the optical surface, and that the cylindrical optic referred to is, although it need not be, a mirror.

The instant invention provides that the cylindrical mirror be mounted on the rotating spindle of a precision numerically controlled lathe by way of an adapter. The especially structured adapter has features for rotary seals and fluid transfer passages between the rotating cylindrical mirror and a stationary manifold/seal holder. A fluid connector is retained in the cylindrical mirror and permits fluid transfer between ports in the cylindrical mirror and the adapter. It is here to be noted that only one fluid connector is necessary, because the remaining cylindrical mirror ports can be plugged. A regulated pressurized gas supply is connected to the stationary manifold of the adapter, and the gas supply pressurizes the cylindrical mirror by virtue of the communication of the adapter (i.e., of the stationary manifold thereof) with the fluid connector and the communication of the fluid connector with the cylindrical mirror. Pressure in the cylindrical mirror is predictably varied with radial position of the machine tool, such that local pressure in the passageways where the face (i.e., the optical surface) is being cut will be the same throughout the optical surface and the same as the calculated local pressure in the top of the heat exchanger portion of the cylindrical mirror during the actual operation and use of the cylindrical mirror. The pressure of the regulated gas supply can be controlled by the tool position controller or by a separate controller.

Accordingly, it is an object of this invention to provide a system for replicating the known (i.e., ascertained) coolant flow local pressure in an optical surface of a heat exchanger portion of a fluid cooled cylindrical optic (e.g., a mirror) in preparation for and during the finish figure machining of the optical surface, so that differential pressure deflection of the optical surface is prevented.

It is another object of this invention to provide a system as described hereinabove, wherein the system includes a unique adapter which can be detachably connected to a rotatable spindle of a lathe, which can releasably hold the cylindrical optic, and which has a stationary manifold.

It is still another object of the instant invention to provide a novel fluid flow connector component for the hereinabove described system, wherein the fluid flow connector is removably connectable to the adapter, and wherein the fluid flow connector interconnects the adapter and the cylindrical optic.

It is yet another object of this invention to provide a suitable means for finish figure machining the optical surface of the heat exchanger portion of the cylindrical