US3154627A

US3154627A - Control means for controlling static gas pressures in support means for a reflector of an optical telescope

Info

Publication number: US3154627A
Application number: US130120A
Authority: US
Inventors: Douglas E Wallis
Original assignee: Sir Howard Grubb Parsons and Co Ltd
Current assignee: Sir Howard Grubb Parsons and Co Ltd
Priority date: 1960-08-09
Filing date: 1961-08-08
Publication date: 1964-10-27
Anticipated expiration: 1981-10-27

Description

Oct. 27, 1964 D. E. WALLIS 3,154,627

CONTROL MEANS FOR CONTROLLING STATIC GAS PRESSURES IN SUPPORT MEANS FOR A REFLECTOR OF AN OPTICAL TELESCOPE Filed'Aug. 8, 1.961 2 Sheets-Sheet 1 Filed Aug. 8, 1961 Oct. 27, 1964 D. E. WALLIS ,1 27

CONTROL MEANS FOR CONTROLLING STATIC GAS PRESSURES IN SUPPORT MEANS FOR A REFLECTOR OF AN OPTICAL. TELESCOPE 2 Sheets-Sheet 2 United States Patent 3,154,627 CONTROL MEANS FOR CONTROLLING STA'IEC GAS PRESSURES 1N SUPPQRT MEAN FOR A REFLECTUR OF AN UP'IICAL TELESQGRE Douglas E. Wallis, Newcastle-upon-Tyne, Engiand, as-

signor to Sir Howard Grubh Parsons & Company Linn ited, NeWcastle-upon-Tyne, England Filed Aug. 8, 1961, Ser. No. 130,120 (Jlaims priority, application Great Britain Aug. 9, 1960 8 Claims. ((31. 88-32) This invention relates to control means for controlling static gas pressures.

One application of such control means is in optical reflecting telescopes where the reflector or mirror may be supported on the side remote from the reflecting surface, by an air bag or by a larger number of individual supports each operated by static air pressure. The purpose of such support is to prevent or reduce warping of the reflector.

It is important in such cases that the static air pressure in the air bag or in the individual supports should be maintained constant when the telescope is in a given position, the actual value at which it remains constant depending on the attitude of the mirror.

The object of the present invention is to provide control means for achieving this.

It is a further object of the present invention to provide improved control means for controlling static gas pressure in a container.

The foregoing and further objects and advantages of the invention will be made more apparent as the specification proceeds.

The invention will be further described, by way of example, with reference to the drawings in which:

FIGURE 1 shows a section through a control device in accordance with one embodiment of the invention suitable for controlling the pressure of a static air supply to an air bag or bags supporting the reflector of an optical telescope;

FIGURE 2 is a section on line IIII of FIGURE 1; and

FIGURE 3 is a schematic arrangement showing the application of the control device of FIGURE 1 to the control of pressure in air bags supporting the reflector of an optical telescope.

In carrying the invention into effect in the form illustrated by way of example and referring to FIGURE 1, a control device consists of a casing 1 closed by an end wall 1a at one end and open to atmosphere at the other. Located in the casing 1 is a piston 2, an annular space being left between the piston and the casing. Air is directed into said annular space to keep the piston in spaced relation to the casing so that the piston effectively floats within the casing on a film of air. Air is passed under pressure into the casing between the piston and the casing wall through jets 3. The air for the jets 3 is supplied from a manifold 4 surrounding the casing 1 for part of its length. The manifold is fed with air through inlet connection 5.

The jets 3 are disposed in a plane at right angles to the axis of the casing 1 and may be disposed at an angle to the radial direction as shown in FIGURE 2 so as to produce a rotational component on the piston to cause it to rotate. Air passing through jets 3 flows out to atmosphere at the open end of the cylinder and through passages 6. The piston 2 is recessed opposite the passages 6 so as to provide an anular recess 6a in which the air can collect prior to passing through passages 6.

Beyond the passages 6 in the direction of the closed end of the cylinder the piston carries a further annular recess 7 which provides an inlet annulus for air which is connected to the air bag through the casing. The axial length of the further recess 7 is such that for the full range of movement of the piston, an inlet 8 for the air supply to the air bag is in communication with the recess '7 The position of the piston shown in the drawing approximates to the maximum travel of the piston away from the end wall 1a of the casing 1.

Air entering the further recess 7 passes to a space 9 between the end of the piston and wall in through passages in the piston formed by axial jets 10 which act as stabilising jets to reduce fluctuation in the piston movement. Space 9 is in communication with the air bag through main outlet connection 11.

There is a leakage path for the air from space 9 to an outlet 12 in the casing 1, a variable restriction in this leakage path being formed by a land 13 on the piston, the wall of the casing and the outlet 12 in order that the pressure in space 9 and hence in the airbag can be kept constant. It will be seen that the length of the restriction is dependent on the position of the piston.

Another land 14 on the piston provides an escape path of constant axial length between the piston and casing 1 from recess 7 to outlet 12 irrespective of the position of the piston. Another land 16 on the piston forms in conjunction with the casing a restriction of constant length between opening 6 and recess 7. This restriction prevents any substantial flow beyond opening 6 towards recess 7 or in the reverse direction. This restriction is of constant length irrespective of the position of the piston.

The device can be orientated through an angle from the vertical position so that the pressure in space 9 is a function of the angle of the piston. In the vertical position the total weight acts and when at an angle to the vertical a component of the weight acts.

The static pressure in the air bag can thus be varied by turning the device through an angle. The device is mounted so that its longitudinal axis is parallel to the optical axis of the mirror. Then if the device is moved in synchronism with the mirror the device provides the desired supporting pressure for any attitude of the mirror.

Referring to FIGURE 3 a reflector 17 of an optical telescope is mounted in a housing 18. The reflector is supported in the housing by annular air bags 19. It is also supported laterally along its sides by members 20. The reflector is tilted by tilting the housing 18.

Control devices of the form illustrated in FIGURE 1 are indicated at 21 and these are mounted on the housing 18 so that as the reflector tilts they tilt in synchronism therewith. It is not, however, essential that they be mounted on housing 18 provided they can be caused to move in synchronism with movements of the reflector.

Air from a compressor 22 passes via conduit 23 to a receiver 24 through driers 25, and filter 26. After filter 26 the conduit 23 divides into two separate conduits 23a, 23b. Both conduits contain valves 27, pressure regulators 28 and pressure gauges 29. Conduit 23a passes to inlet manifolds 4 of each control device whilst conduit 23b passes to inlets 8 of the respective control devices.

Air from outlets 11 of the respective control devices passes through conduits 30, 31, 32 to the air bags 19.

With a reflector of the shape shown the static air pressure in the outer bag would be higher than that in the inner bag as it has a greater thickness of material to support.

In the form illustrated the piston is made in two parts 211, 2b of diflerent density materials so that the resultant density of the piston can be varied more conveniently. The length of the piston can also be varied more easily. The device is highly accurate because of the floating piston and the fact that the escape paths for air from q) the casing are of constant length for all positions of the piston and can be used to control the static air pressure to within i A mm. of Water irrespective of wide variations of the air supply to the controller.

In one typical embodiment the piston is 1 /2 diameter and has part 2a of aluminium and part 2b of mild steel. The casing is of mild steel and 4%" long. The jets 3 are formed in two separate rings each containing 6 jets of 0.03" dia. The clearance between the piston and casing and hence the thickness of the air film is 0.001". There are 12 outlet holes 6 each 0.125 dia. and there are 12 outlet ducts 0.125 dia. The stationary jets are six in number and are 0.03 dia. The pressure of the air introduced to manifold 4 is 20 lb./in. and that to inlet 8 is lb./in. approximately. The static pressure in the air bag is 0.91 lb./in. when the axis of the cylinder is vertical.

Whilst the invention has been described using air, gases other than air can be used.

Further, whilst the invention has been described in connection with the maintenance of a constant static air pressure in an air bag for a reflecting telescope it can be used in any circumstances where it is necessary to maintain a sensibly constant static air pressure in one or more containers. In addition or alternatively it can be used to apply a sensibly constant force to a body.

In certain circumstances there may be a tendency for the piston to oscillate depending on the nature of and the volume of the air container and the connecting means. In such circumstances the oscillations may be damped by connecting space 9 to a further chamber through a restriction or orifice.

A baffle may be fitted to the end of the piston to counteract any reaction on the piston due to the impact of air on the end wall 1a. The battles direct the air in a radial direction.

I claim:

1. Means for controlling static gas pressure in a container which means comprise a casing closed at one end by an end wall and open to atmosphere at the other, a piston located in the casing defining an annular space between the piston and the wall of the casing, means including openings disposed in opposition to one another around the casing wall for directing gas, through the said wall to said annular space, in a plane perpendicular to the axis of the casing to maintain the piston in spaced relation to the casing wall for all attitudes of the casing, egress passages for said gas in the casing wall located between the said openings and the end wall of the casing, an inlet for gas whose pressure is to be controlled located in the casing wall between the egress passages and the end wall of the casing, a main outlet for said gas connected to a space between the piston and the end wall of the casing, said outlet being connected to the container, passages in the piston for permitting continuous flow of gas from the inlet to the said space and a variable restriction for bleeding gas from said space to atmosphere, which variable restriction is formed between a land on the piston, the casing wall and a further outlet located between the inlet and the said space, movement of the piston varying the opening of said further outlet.

2. An optical telescope comprising a reflector, a housing therefor and inflatable containers located between the reflector and the housing, control means for maintaining a pre-determined static gas pressure in said containers, mounted on said housing so as to be tiltable with the reflector, means connecting the control means to a container and means supplying gas to said container, said control means comprising a casing closed at one end and open to atmosphere at the other, a piston located in the casing defining an annular space between the piston and the wall of the casing, means, including openings disposed in opposition to one another around the casing wall, for directing gas through the wall of the easing into said annular space in a plane perpendicular to the axis of the casing to maintain the piston in spaced relation to the wall of the casing for all attitudes of the reflector, egress passages for said gas in the said casing wall located between said openings and the end wall of the casing, an inlet for gas to be supplied to the container located in the casing wall between said egress passages and the end wall of the casing, a main outlet for said gas connected to a space between the piston and the end wall of the casing, said outlet being connected to the container, passages in the piston for permitting continuous flow of gas from said inlet to the said space and a variable restriction for bleeding gas from said space to atmosphere, said variable restriction being formed between a land on the piston, the wall of the casing and a further outlet located between the inlet and the space between the end of the piston and the end wall of the casing, movement of the piston varying the opening of said further outlet.

3. Control means as claimed in claim 1, in which the means for directing gas through the wall of the casing and into annular space between the piston and the casing comprise an inlet manifold for gas under pressure, said manifold surrounding the casing for a portion of its axial length, and jets disposed in opposition to one another around the wall of the casing communicating with the manifold and with said annular space.

4. Control means as claimed in claim 1 in which the means for conducting gas through the annular space between piston and casing comprise an inlet manifold for gas under pressure, said manifold surrounding the casing for a portion of its axial length, and jets disposed in opposition to one another around the Wall of the casing communicating with said manifold and with said annular space, said jets lying in a plane at right angles to the axis of the casing but at an angle to the radial direction to produce a rotational component acting on the piston to cause it to rotate.

5. Control means as claimed in claim 1 in which the piston has an annular recess facing, in all positions of the piston, the inlet for gas supplied to the container and the passages for the gas through the piston from said recess to the space between the end of the piston and the end wall of the casing is formed by axially directed jets in the piston.

6. Control means as claimed in claim 1 in which a further land is provided on the part of the piston between the land forming part of the variable restriction and the inlet for gas supplied to the container which further land provides in conjunction with the wall of the casing a restriction of constant axial length for any gas leaking between the said inlet and the variable restriction.

7. Control means as claimed in claim 1 in which a land is provided on the part of the piston lying between the inlet for gas supplied to the container and the egress passages in the casing for egress of gas conducted through the annular space between piston and casing, said land in conjunction with the wall of the casing forming a restriction of constant axial length for any gas leaking between said inlet and said passages.

8. Control means as claimed in claim 1 in which baflie means are fitted to the end of the piston opposite the end wall of the casing to deflect in a radial direction gas entering the space at the end of the piston from the passages in the piston.

References Cited in the file of this patent UNITED STATES PATENTS 1,734,284 Blair Nov. 5, 1929 1,966,841 Zelov July 17, 1934 2,750,952 Best June 19, 1956 2,918,072 Boler Dec. 22, 1959 2,940,463 Balfour June 14, 1960 2,956,761 Weber Oct. 18, 1960 FOREIGN PATENTS 987,988 France Apr. 25, 1951

Claims

2. AN OPTICAL TELESCOPE COMPRISING A REFLECTOR, A HOUSING THEREFOR AND INFLATABLE CONTAINERS LOCATED BETWEEN THE REFLECTOR AND THE HOUSING, CONTROL MEANS FOR MAINTAINING A PRE-DETERMINED STATIC GAS PRESSURE IN SAID CONTAINERS, MOUNTED ON SAID HOUSING SO AS TO BE TILTABLE WITH THE REFLECTOR, MEANS CONNECTING THE CONTROL MEANS TO A CONTAINER AND MEANS SUPPLYING GAS TO SAID CONTAINER, SAID CONTROL MEANS COMPRISING A CASING CLOSED AT ONE END AND OPEN TO ATMOSPHERE AT THE OTHER, A PISTON LOCATED IN THE CASING DEFINING AN ANNULAR SPACE BETWEEN THE PISTON AND THE WALL OF THE CASING, MEANS, INCLUDING OPENINGS DISPOSED IN OPPOSITION TO ONE ANOTHER AROUND THE CASING WALL, FOR DIRECTING GAS THROUGH THE WALL OF THE CASING INTO SAID ANNULAR SPACE IN A PLANE PERPENDICULAR TO THE AXIS OF THE CASING TO MAINTAIN THE PISTON IN SPACED RELATION TO THE WALL OF THE CASING FOR ALL ATTITUDES OF THE REFLECTOR, EGRESS PASSAGES FOR SAID GAS IN THE SAID CASING WALL LOCATED BETWEEN SAID OPENINGS AND THE END WALL OF THE CASING, AN INLET FOR GAS TO BE SUPPLIED TO THE CONTAINER LOCATED IN THE CASING WALL BETWEEN SAID EGRESS PASSAGES AND THE END WALL OF THE CASING, A MAIN OUTLET FOR SAID GAS CONNECTED TO A SPACE BETWEEN THE PISTON AND THE END WALL OF THE CASING, SAID OUTLET BEING CONNECTED TO THE CONTAINER, PASSAGES IN THE PISTON FOR PERMITTING CONTINUOUS FLOW OF GAS FROM SAID INLET TO THE SAID SPACE AND A VARIABLE RESTRICTION FOR BLEEDING GAS FROM SAID SPACE TO ATMOSPHERE, SAID VARIABLE RESTRICTION BEING FORMED BETWEEN A LAND ON THE PISTON, THE WALL OF THE CASING AND A FURTHER OUTLET LOCATED BETWEEN THE INLET AND THE SAPCE BETWEEN THE END OF THE PISTON AND THE END WALL OF THE CASING, MOVEMENT OF THE PISTON VARYING THE OPENING OF SAID FURTHER OUTLET.