US2830381A - Dynamically damped antifriction mounting - Google Patents

Description

M. H MORRIS DYNAMICALLY DAMPED ANTIFRICTION MOUNTING Filed Nov. 14, 1956 April 15, 1958 INVENTORQ MARION H. MORRIS 1% 9 7 ATTORNEYS Mum United States Patent DYNAMICALLY DAMPED ANT IFRICTION MOUNTING Marion H. Morris, Mountain View, Calif., assignor to Sperry-Sun Well Surveying Company, Philadelphia, Pa.. a corporation of Delaware Application November 14, 1956, Serial No. 622,150 4 Claims. (Cl. 33-223 pending application Serial No. 557,165, filed April 9,, 1956. In these two applications there is disclosed a pool of mercury within a spherical cavity on which there is provided a floating assembly. Due to the particular construction of the floating assembly as will be hereinafter described in greater detail, the floating assembly is maintained constantly centered on the pool of mercury. Thus there is provided an antifriction'mounting of universal angular movement type which is substantially free of static friction. I

This mounting is so substantially free of friction that, after the floating assembly has been disturbed and has been set into motion with respect to the housing, an excessively long period of time is required for the floating assembly to come to rest.

It is the primary object of this invention to provide a damping means for the floating assembly.

More particularly, it is the object of this invention to provide, by means of a high intensity permanent magnet suspended in the mercury pool, a dynamic damping for the floating assembly.

The foregoing and other objects of this invention, particularly relating to details of construction, will become apparent from the following description when read in conjunction with the accompanying drawing in which the figure is a vertical section showing a floating assembly including a damping magnet in a pool of mercury in association with an inclination and direction indicating means for a well surveying instrument.

For the well surveying instrument in general, reference may be made to said prior application of Williston and myself and also to the patent of Young No. 2,616,187, dated November 4, 1952. Only so much of the well surveying instrument is shown in the drawing as is necessary for an understanding of the present invention. The other elements not shown herein involve timing means for controlling the time at which one or more photographic exposures may be made, illumination means, and devices for photographing the marked surface of a spherical or other member to give a record from which direction and inclination may be determined.

The inner casing of a well surveying instrument embodying the other elements mentioned is shown at 2, the casing being receivable within a conventional protective casing sufiiciently strong to withstand the high pressures encountered in bore hole surveying. A pair of housing members 4 and 6 are interfitted to provide a spherical cavity 8 presenting a surface non-wettable by mercury, which at its upper end is closed by a glass disc 10 held up 4 V 1C6 in position by ring 12 cemented at 14 and providing a transparent opening 16. The housing members 4 and 6 are cemented together at 18 and are held in the casing by being pressed against a shoulder 20 by means of a threaded ring 22.

A small bore 24 in the housing 6 provides communicatron between the spherical chamber 8 and a fitting 26 threaded into an enlarged bore 25 in the housing 6. A valve member 27 having a central bore 27 is positioned between the end of the fitting 26 and the base of the bore 25. The member 27 is formed of a deformable material such as rubber. When the valve member is compressed between the fitting 26 and the base of the bore 25, the bore 27' in the valve member 27 closes.

The useof the valve member 27 and the filling and evacuation of the chamber 8 forms no part of the present invention and reference may be made to my prior application Serial No. 557,165 for details involved in these procedures.

A float'assembly is located within the cavity 8 and comprises a hemispherical body 28 which may be formed of 1 a plastic material such as nylon. Located under the hemispherical body 28 is a ring 30 of plastic material having on its exterior cylindrical surface a ribbon of metal 32 which in the preferred embodiment of the invention is platinum though other metals may be used. The assembled ribbon 32 and ring 30 are pressed into a recess provided in the bottom of the body 28 and held therein by Nichrome wire pins 34. The inner surface of the ring 30 is conically tapered as indicated at 36.

The float assembly just described is supported by a ool of purified mercury 38, the volume of mercury being approximately half the volume of the cavity 8, and at any rate being such as to support the float with its spherical surface closely concentric with the spherical surface of the cavity 8.

Secured to the underside of the body 28 by pins 40 is a base 42 of a pedestal having a stem 44 extending downwardly into the pool of mercury 38. A magnet bar 46 forming a compass needle is afiixed to the lower end of stem 44 by means of a screw 48 and is thus positioned within the pool of mercury 38. After the bar 46 is oriented with the North-South marking on the hemispherical body 28, the bar 46, the stem 44 and the screw 48 are cemented together as indicated at 50. Desirably, the base 42 and the stem 44 are formed of a non-magnetic material such as aluminumand the compass bar 46 is an Alnico magnet plated thinly with a silver coating.

As previously noted, the float assembly is supported by the pool of mercury and a condition of equilibrium exists, maintaining the float centrally located, which is apparently due to a considerable extent to the fact that mercury wets the platinum surface which it contacts and does not wet the inner conical surface 36 of the plastic ring. Thus, surface tension action tends to pull the float downwardly into the mercury in excess of the degree of immersion which would result solely from the weight of the float. Under these conditions, equilibrium is attained only when the float is centrally located. Any tendency to move transversely results in an elevation of the center of gravity of the system by displacement of mercury, and hence reliable return to the central equilibrium position is assured. By reason of the non-contamination of the mercury surface, there is furthermore produced, to the extent to which observation may be made, a complete absence of static friction. In other words, in response to a magnetic field, the float will assume an azimuthal position to an extremely high degree of accuracy.

The conditions involved in the maintenance of this condition of equilibrium are more fully set forth in the 3 above mentioned application of Samuel H. Williston and myself, Serial No. $51,024.

It should be noted that the weight of the floating assembly is adjusted so that the upper edge 31 of the mercury meniscus adjacent to the platinum ribbon 32 is positioned below the bottom of the nylon body 28. Thus, the meniscus is freeto seek its own level against the platinum ribbon without interference from the nylon body.

It will be evident when the compass needle 46 is displaced from a North-South position, the earth's magnetic forces will cause it to seek a North-South position. Due to the low friction of the mounting and the inertia of the float, there is a tendency for the floating assembly to oscillate. Tilting oscillations also occur about the position of equilibrium. f

However, by employing a high intensity magnet such as an Alnico magnet and positioning the magnet in the mercury pool 38 as shown, movement of the magnet within the pool generates eddy current in the mercury.

This generation of eddy currents dissipates the inertial energy of the float assembly and thus provides a true dynamic braking. The effect of the structure is to provide a highly damped and extremely low friction mounting.

It will be noted that the hemispherical body 28 is solid and thus if the body is caused to assume the position rotated on a horizontal axis 90 from that shown in the drawing the pool of mercury will apply force not only downwardly against the inner surface 36 of the ring 30 but also horizontally against the lower half of the under surface of the body 28. The force of this mercury acting against the body 28 will cause the body to rotate and to assume a floating position such as that shown in the drawing. Were the hemispherical body hollow this would not occur due to the fact that the pressure of the mercury would be acting downwardly over a major portion of the surface of the body with which it would be in contact and it would thus press the body against the inner wall of the spherical cavity 8 with such force as to prevent its rotating and assuming a floating position. Thus, in handlingor when undergoing rapid movement, the float assembly always aligns itself promptly in a floating position. This construction in combination with the magnetic damping provides a reliable and highly damped extremely low friction mounting for a magnetic compass or other floating.

apparatus.

While the invention has been described herein as emeluding a magnetized member submerged in said pool of mercury providing dynamic damping of movement of said floating means on said pool of mercury.

2. Apparatus comprising a pool of mercury, means floating on said pool of mercury and freely rotatable thereon, said floating means including a magnetized member submerged in said pool of mercury providing dynamic damping of rotary movement of said floating means on said pool of mercury.

3. An antifriction mounting comprising a container presenting a surface non-wettable by mercury, a pool of mercury in said container, and a float assembly in said pool .of mercury presenting to the surface of the mercury a solid surface having characteristics such that at a line of contact the mercury has a meniscus that is concave upwardly and said float assembly including magnetized member submerged in said pool of mercury providing dynamic damping of movement of said floating means on said pool of mercury.

4. Antifriction mounting comprising a container presenting a surface non-wettable by mercury, a pool of mercury in said container and a float assembly in said pool of mercury presenting to the surface of the mercury a solid surface having characteristics such that at a line of contact the mercury has a meniscus that is concave upwardly and said float assembly including a rotatable magnetized member submerged in said pool-of mercury providing dynamic damping of movement of said floating v means on said pool of mercury.

References Cited in the file of this patent UNITED STATES PATENTS 1,294,710 Roland Feb. 18, 1919 1,397,490 Peradotto Nov. 15, 1921 1,912,358 Bush June 6, 1933 2,765,541 Story Oct. 9, 1956

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