US2928709A

US2928709A - Externally pressurized fluid bearing

Info

Publication number: US2928709A
Application number: US545266A
Authority: US
Inventors: Heard K Baumeister
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1955-11-07
Filing date: 1955-11-07
Publication date: 1960-03-15
Anticipated expiration: 1977-03-15
Also published as: FR1172048A; DE1256696B

Description

March 15, 1960 H. K. BAUMEISTER 2,928,709

EXTERNALLY PRESSURIZED FLUID BEARING 2 Sheets-Sheet 1 Filed Nov. 7. 1955 FIG.2

INVENTOR. I HEARD K. BAUMEISTER god 11w FIG.3

AGENT March 15, 1960 H. K. BAUMEISTER 2,923,709

I EXTERNALLY PRESSURIZED FLUID BEARING Filed NOV. 7, 1955 2 Sheets-Sheet 2 FIG.5

55 INVENT m 54 HEARD K. BAUM ER BY Z AGENT 2,928,709 1C6 Patented Mar. 15, 1960 EXTERNALLY PRESSZED FLUID BEARING Heard K. Baurneister, New York, N.Y., assignor to Intel-national Business Machines Corporation, New York, N.Y., a corporation of New York Application November 7, 1955, Serial No. 545,266

2 Claims. (Cl. 346-74) This invention relates to slider bearings of the externally pressurized type and more particularly to floating shoe type bearings adapted to support a magnetic recording head.

Heretofore, magnetic recording heads have been supported by air bearings utilizing the familiar Bernoulli effect. This type of air bearing'comprises a shoe having a surface, referred to as the sill surrounding a recess referred to as the pool, which is in juxtaposition with a moving surface such as a rotating magnetic drum or disc. Air is supplied to the shoe by means of a hole bored therethrough and oriented orthogonally to the sill area surface. The air is supplied to the bearing surfaces at a constant pump pressure, the force provided by the air in the pool and from the high velocity escaping air over the sill, opposes the force of the atmosphere on the other side. The shoe exists at a predetermined distance from the drum when these forces are substantially equal. When the relative velocity of the surfaces is zero, for example, and the spacing therebetween is large, the wellknown Bernoulli effect causes a reduction in pressure over the sill area so as to permit a decrease in the spacing. However, when the spacing is small there exists a more linear pressure gradient over the sill area which forces the surfaces apart until the sill and pool pressures and the external atmospheric pressure are equalized, and the shoe reaches a stable position.

Thus although the pressure of the air supplied to the shoe is constant, it tends to maintain a predetermined distance between the surface of the shoe and the surface of the magnetic drum.

The chief disadvantage of the Bernoulli type bearing referred to above is that the pump pressure and therefore the pool pressure is substantially constant. Another disadvantage is that the spacing between the shoe and the drum is rather large. A further disadvantage exists in that the maximum force which can be utilized to maintain a constant spacing by such a shoe operating in atmospheric pressure is quite small and could never be greater than 14.7 lbs. per square inch.

Accordingly, it is an object of the present invention to provide a novel bearing capable of utilizing a force in excess of that fraction of 14.7 lbs. per square inch, which due to the inertia of the shoe and eccentricity of the drum, will thereby maintain a more constant spacing and also permit a smaller spacing.

Briefly, the present invention comprises a shoe having a bearing surface which coacts in a very different manner than before with a moving surface, as for example, a rotating magnetic drum, disc or tape, etc. The bearing surface of the shoe, referred to as the sill area, intersects a recessed chamber or pool encompassed by the shoe. A lubricant under pressure is supplied through a restrictor to the pool. With the drum at rest, for example, the shoe assumes a stable position where the effective pressure P (gauge) in the fluid over the whole shoe area A.

is sufficient to sustain the externally applied loading force F. The effective pressure P is due to the pool pressure and the hole.

1" and the sill pressure P A change in the distance between the surface of the drum and the bearing surface of the shoe permits an alteration in the effective pressure to occur whereby the force exerted against the drum causes the shoe to move towards the stable position. For any position of the shoe other than the stable position, the pressure in the pool and over the sill changes in such a manner that the product of the effective pressure times the shoe area is temporarily different from the externally applied loading force F. This imbalance of the forces tends to move the shoe towards the stable position.

Thus since the effective pressure in the pool as well as over the sill is capable of changing and does not need to be in any part constant, the bearing tends to maintain very closely a predetermined distance between the shoe and the drum. The presence of the restrictor allows the pool pressure P to change without requiring that the pressure at the pump or source of the lubricant be altered.

The load carrying capacity of the bearing can be increased by increasing the pump pressure. In addition, since the novel bearing is capable of supporting greater loads than a similar Bernoulli type bearing, the spacing between the novel 'shoe .and the drum may be smaller than is permissible with the Bernoulli type bearing.

'Since the sill area of the present invention may be smaller than presently known shoes the coefficient of friction between the bearing. surfaces. could be made smaller.

One embodiment of the invention includes a novel restrictor which may be incorporated within the structure of the shoe. The restrictor includes a removable plug assembly which may be removed so that the restrictor can be cleaned or easily'changed. The novel restrictor includes the dumbbell-shaped plug having a center rod and two larger ends which is inserted into a hole drilled into the shoe. The diameter of the rod is slightly smaller than the diameter of the hole so that the fluid lubricant may flow in the space between the peripheries of the rod The larger ends merely serve to center the rod in the hole. The amount of restriction to fluid flow provided by the restrictor is governed by the amount of space existing between the rod and the inside diameter of the hole.

Another object is to provide an improved externally pressurized shoe type hearing which maintains a predetermined distance between the bearing surface of the shoe and the bearing surface coacting therewith. V

A further object is to provide a novel multi-pad externally pressurized bearing capable of operating with air or oil as the fluid lubricant.

It is also an object to provide a recording head which floats on and follows a magnetic surface despite displacements due to the eccentricity and non-circular cross section of the drum, disc, tape drive capstans, etc.

Another object is to provide a highly stable air lubricated shoe for supporting a recording element.

A still further object is to provide an externally pressurized slider bearing having one or more pads, each pad having a restricter coasting therewith whereby a change in the distance between the bearing surfaces causes a change in the pressure of the lubricant within each pad so as to restore the bearing to a stable parallel condition.

A further object is to provide a novel restrictor.

It is also an object to provide a novel restrictor which is considerably smaller than a restrictor composed of coiled tubing.

Another object is to provide a novel restrictor which supplies two pools simultaneously.

An additional object is to provide a restrictor contained within a bearing block or shoe so that the restrictor is not susceptible to fracture as is the case with a copper tubing restrictor which is constructed external The lubricant enters the shoe at the point 36 and exhausts through the spacing 37 between the surface of the Another object is to provide a restrictor which acts as a filter to lodge dirt and dust particles and which is capableof being cleaned so as to remove any particles filtered outof the fluid lubricant.

Another object is to provide a novel restrictor which is incorporated within a bearing plug or shoe wherein said shoe defines ahollowdiameter comprising a first member of-the restrictor and a secondmember which is designed to fill a substantial portion of the volume of said first member and said restrictor being provided with inlet and outlet means whereby a fluid lubricant is supplied to and removed from the restrictor.

Another objectis to provide a novel externally pressurized, fluid lubricatedbearing including a shoe having a bearing surface which includes a chamber, a restrictor and means for. supplying a pressurized fluid lubricant through said restrictor to said chamber and thus to'the bearing surfaces.

shoe '27 and the surface of the drum 21. As will be explained presently, the exhausting lubricant causes a predetermined spacing to be maintained between the bearing surfaces of the shoe and the surface of the drum. The distance between the bearing surface of the shoe and the surface of the drum is dependent upon the external loading force applied to the shoe 27 by means of the leaf spring .24 and the pressure of the. fluid supplied to the sho It is not necessary to provide a retracting mechanism for lifting the shoe off of the drum when the drum is Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle. In the drawings: V Fig. 1 illustrates the novel hearing which incorporates a single pad and utilizes an external restrictor;

Fig. 2 is a cross section of Fig. l and thus illustrates the internal construction of the bearing; I Fig. 3 illustrates the equivalent electrical circuit of the mechanical system of Fig. 2;

Fig. 4 illustrates a novel bearing which incorporates a plurality ofpads and an internal restrictor;

Fig. 5 is 'a cross section of Fig. 4 and illustrates the" which is not illustrated. A mounting bar 22 is provided which is rigidly attached to any suitable external-framework. A leaf spring 24 is fastened to the underside of the mounting bar 22 and extends towards the surface, of the drum in a substantially tangential direction. Leaf spring 24 is pro-stressed or pre-bent. The other extremity of the leaf spring 24 is bifurcated and the

separate extensions

25 and 26 span the shoe 27 and encircle a pair of trunnions 28 which extend from the shoe 27. The mounting bar 22 is secured to the external mechanism not shown or described herein so that the leaf spring 24, which may be pre-bent, applies a loading force to the shoe 27 which tends to force the shoe toward the surface 21 of the drum. e

A magnetic recording element or transducer 30 is mounted on the shoe 27 so that the gap of the yoke 31 is adjacent to the recording surface 21. The head structure is fastened to the shoe by means of set screws which clamp the laminated yoke 31 against one side of the shoe. The yoke may also be mounted on the shoe in any other conventional manner.

A fluid lubricant at a constant pressure is supplied to the pipe 34 and through the'restrictor ,35 to the shoe.

stopped, providing that the fluid lubricant is continuously supplied to the head. The presence of the flowing lubricant maintains a predetermined spacing between the head and the recording surface even when said surface isstationary. Thus when the drum is stopped the shoe cannot mar or score the drum surface.

The escaping air aids in preventingthe' accumulation of dirt in the spacing between the head andthe drum.

Due to possible eccentricities of the drum 20, the shoe 27 may be subject to rocking motions about the trunnions 28 and also tomotion about the axis 23. This flexibility permits the shoe 27 to maintain a constant space relationship between the surface of the shoe and the drum 21 despite irregularities which may appear along the drum surface. Furthermore, the shoe 27 is capable of a tipping motion due to the

individual extensions

25 and 26 of the leaf spring 24. It should be appreciated that mechanisms other than the leaf spring 24 and the mounting bar 22 may be. used to suspend the shoe 27 over the drum surface. Fig. 1 may be supported by the type of mounting illustrated in Fig. 3 of application Serial No. 406,448, filed January 27, 1954 by H. K. Baumeister.

Referring more particularly to Fig. 2, a cross section of rearward portion of the shoe 27 is illustrated. The extremity ofthe restrictor 35 of Fig. 1 is connected to the shoe27 at the point 36 as indicated in Fig. 2. The fluid lubricant flows downward through a channel 01' hole 40*extending through the shoe to a pool or chamber 41. f

The poolis also referred to as a lubricating pad. After filling the pool 41, the lubricant exhausts at the points 37 between the'bottom surface of the shoe and thesurface 21 of the'drum. The pool 41, which is recessed in the bottom surface of the shoe 27, may comprise a volume of any suitable configuration. The bottom surfaces 42 of the shoe 27 which are not recessed are referred to as sill areas.

In order for a predetermined space relationship to be maintained between the surface 42 of the shoe and the drum surface 21, the externally applied force F must be equal to the effective pressure P times the area A of the shoe which is juxtapositioned with the drum surface. When this relationship is disturbed, the space relationship betweenthe shoe and the drum recording surface will be increased or decreased. In order for the shoe to be returned to the stable position wherein F is equal to PA,.the effective pressure must be altered so that it is properly increased or decreased as required. The area of the bottom surface of the shoe comprises the 'sill area A and'the pool area A,,. The efiective pressure P of the lubricant which is exerted against'the surface of the drum is due to the pressure beneath the sill areas P and the pressure P which exists within the For'example, the shoe 27 of If, for example, the spacing between the surface of the shoe and the drum surface is decreased temporarily, the effective pressure P must be increased so as to provide a greater force which will tend to restore the shoe to its normal stable position. Also, when the distance between the shoe and drum surfaces is increased temporarily, the effective pressure must be decreased so that the shoe will tend to return to its normal stable position, thereby decreasing the spaced relationship of the shoe and the drum to the normal distance. A change in the distance between the drum and shoe bearing surfaces causes the sill pressure P and the pool pressure P to be adjusted so that the shoe is restored to its normal stable position. The presence of the restrictor 35 of Fig. 1 permits the pool and sill pressures to be adjusted even though the pressure at the source of the lubricant remains constant. The removal of the restrictor prohibits the shoe from functioning in the manner described above.

Referring more particularly to Fig. 3, the electrical analogy of the single pad shoe of Figs. 1 and 2 is illustrated. The resistance B is a function of the restriction or resistance to fluid flow provided by the restrictor 35 of Fig. l and the resistance R is a function of the separation 37 (Fig. 2) between the shoe and drum surfaces.

The voltage V of Fig. 3 is related to the pressure at the pump or source of lubricant and is considered to be a constant. The voltage V is a function of the pool pressure P The current flowing through the resistors B and R is a function of the quantity of fluid lubricant supplied to the shoe of Figs. 1 and 2. It is apparent from the electrical analogy that the maximum change in P with respect to the factor R occurs when the mechanical design of the shoe is such that the factors R and B are equal. It is desirable to obtain the maximum change in the pool pressure 1? with respect to the separation of the drum and shoe surfaces in order to obtain a highly sensitive bearing. It is desirable that the bearing of Figs. 1 and 2 be highly sensitive so that a change in the distance between the shoe and drum surfaces is corrected and the shoe returned to its stable position as rapidly as possible.

The electrical analogy also points out that the purpose of the restrictor is to permit a pressure drop to occur between the source of the lubricant and the pool or pad of the shoe. The pressure within the pad must be capable of increasing or decreasing as the spacing between the bearing surfaces changes. That is, when the spaced relationship of the surfaces is increased due to an irregularity in the surface of the drum, the pool pressure must decrease and similarly, when the spacing is decreased, the pool pressure must increase so as to reestablish the stable position of the shoe. The restrictor could be removed from the system only if the constant pressure source of lubricant is replaced by a device which provides a constant quantity of lubricant flowing in the system. Since it is diflicult to provide a constant quantity lubricant source, the use of the restrictor considerably simplifies the system and the external pumping apparatus which must be used to supply the fluid lubricant.

Since the externally applied force F is equal to the product of the effective pressure and the area of the shoe, it is apparent that by increasing the load applied to the shoe, the spacing between the bearing surfaces of the shoe and the drum can be decreased.

The externally pressurized bearing described herein operates satisfactorily where the lubricant is air, oil or another suitable fluid. The description hereinabove of the operation of the bearing of Figs. 1 and 2 applies asserts 6 lubricant is air but will not operate in suitable manner when the lubricant is changed to oil.

It has been determined experimentally that when the shoe of Figs. 1 and 2 is provided with a relatively wide sill area in the direction that the recording surface is moving, a cubic relationship exists between the resistance to flow of the lubricant between the bearing surfaces and the spacing between said surfaces. As the sill area is made'smaller and approaches a knife edge, the relationship between the resistance to flow and the spacing of the bearing surfaces is a square or even a direct relationship depending on the fluid properties. son, the resistance to flow in a shoe having a wide sill area is C /h whereas the relationship is Cg/h when the sill area is very narrow, where C and C are arbitrary constants and h is the distance between the bearing surfaces of the shoe and the rotating drum. Accordingly, it is apparent that where the resistance to flow is inversely proportional to the cube of the spacing between the bearing surfaces, a given change in spacing h, produces a greater change in the pool pressure P than would occur where the relationship Cg/h obtains. This aids in making the head more sensitive to changes in spacing and thus is another factor which increases the sensitivity of the shoe.

' Referring to Fig. 4, a second embodiment of the invention is illustrated which incorporates within the head a novel restrictor. It is apparent that when the restrictor comprises a long section of coiled tubing as shown in Fig. 1, difliculties are encountered in mounting the assembly on the head since the tubing is subject to fracture. Furthermore, the restrictor 35 of Fig. 1 occupies a space which is often quite large compared to the space required by the shoe and head assembly.

These difliculties are overcome by constructing the restrictor within the shoe as indicated in Figs. 4 and 5 :hich illustrate a restrictor supplying two pools with no greater difficulty than would be required to supply a single pool. In Fig. 4 the lubricant under constant pressure is supplied to the tube 46 which is connected directly to the shoe at the point 48.

Fig. 5 is a cross section of the shoe 47 of Fig. 4 taken at the point indicated. In Fig. 5 the tubing 46 which carries the fluid lubricant is suitably connected to the 7 shoe 47 at the point 48 by means of a threadable connection or other well-known methods. The fluid contained within tube 46 flows downward through the channel or hole 49 to the restrictor.

The restrictor comprises a hole 52 extending into or through the shoe 47. The hole is threaded at the points 53 so as to accept the threaded caps 55, which, in this design, are used to seal the ends of the hole. A dumbbell assembly 54 is inserted into the hole and retained therein by the caps 55. The dumbbell assembly 54 is illustrated in Fig. 6. The rod 56 is connected to the

collars

57 and 58 which serve to center the rod in the hole 52. The diameter of the rod 56 must be slightly smaller than the inside diameter of the hole 52 so as to provide a predetermined clearance therebetween. The diameter of the

collars

57 and 58 is sufiiciently smaller than the diameter of the'hole 52 to allow the plug 56 to be inserted therein. The difference between the diameter of the rod 56 and the hole 52 determines the resistance to flow of the lubricant flowing through the restrictor. As the diameter of the rod 56 is decreased, the resistance to flow offered by the restrictor to fluid flow is decreased.

The fluid lubricant applied to the restrictor through inlet hole 49 of Fig. 5 flows through the space 52 existing between the periphery of the rod 56 and the hole 52 and exits through the outlet holes 60 and 61. These outlet holes connect the restrictor with the pools or

pads

62 and 63. A pressure drop may occur across each half of the restrictor so that the pressure in

pools

62 and 63 is lower than the pressure existing in the supply tube 46 and the inlet hole 49. The fluid then escapes from the By way of comparispasm-a P9 15 and 6 t o h the s ce- 37 xi n e een the bearing surfaces of the shoe and the magnetic drum.

it is to be noted that the restrictor illustrated in Fig. 5 serves both of the

pools

62 and 63. It is apparent that if a shoe contains a single pool, the restrictor of Fig. 5 could be used by merely placing the inlet hole 49 at the opposite extremity of the restrictor from the location of an'outlet hole such as outlet hole 60. Other variations of the restrictor arealso possible depending upon the construction of the shoe. For example, the restrictor might also be constructed in'a vertical position so that the cap 55 of Fig. 5 appears in the topsurface of the shoe assembly. i

Afirst advantage of'therestrictorof Figs. 5 and 6 is that it is considerably smaller than restrictors now known in the. art of lubrication engineering." For example, a

magnetic transducer in spae'ed relationship with a recording surface" including the'combination er, aia pidly,

moving bearing surface, a bearing shoefh'aving a recess, a magnetic transducer supported'by said shoe and ar; ranged in spaced relationship with respect to said moving bearing surface, means urging said shoe against said bearing surface, a second bearing surface surrounding said recess and existing in juxtaposition with said first surface to float thereon, an external source of pressurized lubricant, and means for'supplying said lubricant to said recess of said'shoe thereby creating a force in opposition to the urging means .so that said shoe floats on said' bearingjsurface including means for effecting an adjustment of the pressure of the lubricant within said recess in response to a change in separation between'said second bearing surface and said first bearing surface to restrictor. of the type illustrated in Fig. 5 having a total 7 length of one inch and a radial clearance of 0.001inch will provide a resistance tofluid flow substantially equal to that provided by a coiled copper tubing restrictor of the type illustrated in Fig. 1. which comprises approximately 477 feet of tubing, having an inside diameter of 0.1 inch. The restrictor of Fig. 5 is also equivalent to a restrictor comprisingta hole having a diameter of 0.0135 inch and approximately 12.4 inches long. The latter type restrictor is impractical and difficult to construct.

A further advantage of the restrictor of Fig. 5 lies in the factthat it can be constructed within the shoe 47 and thus is not subject to damage or fracture as is the case with an exposed coiled tubing restrictor of the type illustrated in Fig. 1. Where the hole 52 of Fig. 5 has a diameter of approximately 0.25 inch item be drilled and reamed in the shoe'within very small tolerances. Likewise, the plug 54 can be machined to small tolerances so that the difference between the diameters of the rod 54 and the hole 52 is of the order of 0.001 inch.

Another advantage of the novel restrictor of Fig. 5

is that the plug assembly of Fig. 6 can be removed for cleaning purposes. It is frequently impossible to clean a restrictor of the type illustrated in Fig. 1 which has become clogged by large dirt particles.

An additional advantage of the restrictor described 1 vention as applied to a preferred embodiment, it will be understood that'various, omissions and substitutions and changes in the form and details of the deviceiillustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is: r

1. In a magnetic recording system for supporting a counteract said change, the said adjustment effecting means being contained within said bearingshoe, the said shoe defining a substantially cylindrical chamber of pre: determined length having fluid entry and exit pcrts, a longitudinal member having a s'rnaller' diameter 'than said chamber and inserted therein to provide a spacing between the outer surface of said longitudinal member and the inner surface of said chamber in the range of one to five thousandths of an inch, and means for main taining a predetermined distance between the periphery of said longitudinal member and the inside surface of said chamberto provide a pressure differential between said entry and exit ports, whereby the spacing between said shoe and said recording surface is maintained submember contained within said chamber and occupying a smaller volume for producing a pressure differential between said pad and said source whereby a change in spacing between said, recording surface and the surface of said first member is counteracted by'a change in said pressure differential to adjust the pressure in said pad thereby re-establishing the original spacing between said transducer and said recording surface.

References Cited in the file of this patent UNITED STATES PATENTS 1,619,444 Taylor Mar. 1, 1927, 2,038,216 Harrison et al. Apr. 21 1936 2,415,992 Clair Feb. 18, 1947 2,612,566 Anderson Sept. 30, 1952 2,695,199

Blizard Nov. 23, 1954-