GB2111873A - Rotary index table with fluid pressure preloaded bearings - Google Patents

Abstract

Rotary tables for machine tool application are disclosed of the type using "Hirth" couplings to provide precision indexed positions and which are characterized by an hydraulically actuated piston member, 78 one set of mating serrated teeth 22 carried by the rotary table and a concentric row of teeth fixed to the table base (16) with the rotary table being supported on bearings. A series of ball bearings 32 are disposed in corresponding ball grooves (34), with a built-in predetermined amount of clearance in the bearing to enable the coupling teeth to be seated without interference from the bearing. Fluid pressure is applied in the cavity 142 to disengage the piston 78 and to move the table top plate 14 away from the base so as to preload the ball bearing, in order to provide a precision rotation of the rotary table. The table top plate is also formed with an outboard bearing surface engaged with a surface on the base when the serrated teeth are locked for maximum support, but are lifted clear when released to reduce wear and friction during indexing rotation of the top plate. In a second embodiment, the rotary table top assembly is mounted on bearings having a friction characteristic decreasing with increasing pressure until an optimum preload level, disengaging air pressure is applied so as to increase the pressure on the bearing during indexing rotation of the table. <IMAGE>

Description

SPECIFICATION Rotary index table with fluid pressure preloaded bearings Background of the invention This invention concerns rotary tables, and more particularly, rotary tables of the type employed in the machine tool industry for mounting of work pieces for precision indexing or rotation of the work pieces during machining or other operations.

Rotary tables have in the past, been designed employing the so called "Hirth" couplings, which consist of mating circular rows of teeth carried by the rotary table and by an axially movable member mounted within the table base, either hydraulically or pneumatically actuated to move into and out of engagement with the teeth carried by the table.

Index positions are achieved in each mating position of the Hirth coupling teeth, while the member carrying the teeth is moved into engagement and retracted by hydraulic pressure and counteracting springs.

Such an arrangement is disclosed in U.S. Patent Application Serial No. 149,906, filed May 15, 1980 by the present inventor.

Hirth couplings have been found to provide great accuracy in each indexed position, which accuracy increases with wear due to the characteristics of the mating engagement. In addition, great rigidity in each indexed position is afforded by the mating teeth, which rigidity offers a great advantage in the context of machining work pieces.

Afurther refinement of this concept involves the provision of double rooms of mating coupling teeth, with the axially movable member formed with concentric circular rows of teeth, one row mating with a corresponding circle of teeth carried by the rotations table member or top plate and the other teeth set engageable with a corresponding circle or row of teeth fixed to the table base. By having differing numbers of teeth in the respective inner and outer rows, a vernier-like effect can be achieved which, can achieve enormous numbers of indexed positions, each of which are highly accurately repeatable. In this instance, the axially movable member is rotated as well as the rotary table plate.

An example of such a table is shown in U.S. Patent Application Serial Number 244,589 filed March 17, 1981, also by the present inventor and assigned to the same assignee of the present application.

As described in that application, an axially movable piston member carrying the double row of Hirth coupling teeth is engaged by hydraulic pressure and disengaged by air pressure, which air pressure provides a rapid disengagement.

There is an inherent problem in using an indexing type table utilising Hirth couplings as a non indexing rotary table, usable for contouring. This problem is due to the nature of the Hirth coupling and the physical arrangement of the table in being supported on rotary bearings. As the piston member moves into engagement with the table top plate and fixed gear teeth, the mating teeth, should desirably be allowed to freely seat, both radially and axially. If the rotary bearing resists full seating of the teeth, accuracy is adversely affected.

Accordingly, it is usual to provide "play" in the table bearing which enables the Hirth coupling to fully seat and to not create an interference by the constraint of the bearing. Contrariwise, with the table in the unlocked position, the table rotation is inherently not precise due to the aforementioned play in the bearing.

A costly alternative approach is to machine the bearing raceways to locate the bearing pitch line to the pitch line of the Hirth coupling teeth in the locked position.

In any event, there has not heretofore been provided a precision, freely rotatable table combined with a precision indexing table utilising such Hirth coupling teeth for providing the indexed positions.

Sometimes the machining forces are relatively heavy, such as in broaching operations, and with the work place supported on the table this tends to create excessive deflection in the table bearings and other parts. It would thus be highly desirable to provide maximum rigidity to the table top plate in the locked position.

This rigidity could be provided by providing mating surfaces at the maximum radial outboard rotations underneath the table and the table base with the table top plate in the locked position. This has heretofore been difficult to achieve due to the need for the Hirth coupling teeth to freely seat causing the table top plate to be axially shifted during seating.

In addition, if such mating surfaces were provided, the faces would wipe during indexing, increasing the power required to rotate the table due to friction and the mating surfaces would be subject to wear which would lead to inaccuracies after extended use.

There is also known, a bearing material which is sold under the trade name, "TURCITE", which has been useful for bearing applications for lower cost rotary tables, in which the table is simply supported on flat rings of such material. here are difficulties involved in designing the bearing, due to a peculiar characteristic of the material. Under lightly loaded conditions, the friction of the bearing increases rather than decreases until a predetermined load is carried by the bearing. This predetermined preloading is difficult to achieve at the optimum level.

It is an object of the present invention to provide a rotary work table of the type described in which both a precision indexing function and a precision non indexing rotation mode is possible.

It is a further object of the present invention to provide such indexing precision rotation table which does not require costly bearing constructions for support of the table top plate.

It is yet another object of the present invention to provide such a rotary table in which the table top plate is supported on mating radially outermost surfaces in the indexed locked position, which, during indexing rotation are lifted clear of engagement to eliminate wear and drag on mating surfaces, while enabling full seating of the Hirth coupling teeth without interference.

It is still another object of the present invention to provide a rotary indexing table which enables reliable full seating of the Hirth coupling teeth without requiring precision bearings.

It is still another object of the present invention to provide a rotary table of the type described in which a carefully controlled preload on the bearings is provided, such as to enable proper performance when utilising bearing material requiring a predetermined load and also to control the bearing load during rotary indexing to minimise the wear thereof.

Summary of the invention These and other objects of the present invention which will become apparent on a reading of the following specification and claims are achieved by an arrangement whereby the bearings are preloaded by fluid pressure supplied to a cavity within the table housing tending, to produce controlled preloading of the bearings supporting the table top plate. In each embodiment, the preload fluid pressure is also exerted in the cavity whereat the Hirth coupling teeth are located, to disengage the Hirth coupling teeth by forcing the movable piston member axially away from the engaged position and which preloading fluid pressure is overcome by the higher actuating pressure applied during locking of the rotary table.

In the first embodiment, the fluid pressure is applied to a space immediately below the table top plate adjacent the Hirth coupling teeth tending to lift the rotary table top plate which is supported on a set of bearing balls disposed in corresponding groove machined into the periphery of a circular plate to which the rotary table top plate is affixed and in an outboard fixed gear ring secured to the table base, such that the upward fluid pressure acts to exert an upward or outward fluid pressure which acts to preload the bearing balls. The rotary table top plate itself is affixed to a circular coupling gear plate bearing the Hirth coupling teeth and overlies both the upper surface of the coupling gear plate and the upper surface of the fixed ring.An annular movable piston member is mounted around an annular pedestal member affixed to the coupling gear plate and which carries two concentric circular rows of teeth movable into respective engagement with the table top plate teeth and a second row of teeth machined into the undersurface of the fixed gear ring.

The space beneath the piston is also defined in part by a flange carried by a drive tube connected to the table top assembly such that upon application of hydraulic pressure in the space, the table top plate is drawn downwardly to overcome the bearing preload fluid pressure while the piston moves upwardly to engage the double row of Hirth coupling teeth.

The ball bearing is designed with a degree of radial or axial play sufficient to enable full and free seating of the Hirth coupling teeth with the bearing unloaded.

Removal of the hydraulic pressure enables the re-exertion of the air pressure, forcing the table top plate upwardly, with the bearing preload causing disengagement of the mating undersurface of the table top plate and the upper surface of the fixed tooth ring. The upper surface of the fixed tooth ring and the under surface of the table top plate are manufactured to be in precise alignment with the plane produced with the Hirth coupling teeth in the locked position.

The pitch plane is precisely located by removing the rotary table top plate and machining across the upper surface of the coupling tooth plate and the tooth fixed ring with the Hirth coupling engaged, providing precise parallelism between these surfaces and with the coupling pitch plane. The table top plate is then reassembled which brings the under surface thereof into position atop the upper surface of the fixed tooth ring such that the table top plate is supported at a radially outermost position on the upper surface of the fixed tooth ring in the locked or indexed position, while enabling the creation of the gap there between upon application of the preloading fluid pressure.

In the second embodiment, the table top plate is supported on a "TURCITE" bearing material and the preloading pressure acts in a downward direction such as to force the table into tight engagement with the "TURCITE" bearing and with the regulated fluid pressure enabling precise control over the preloading, such as to provide optimum reload for the bearing material characteristics.

Brief description of the drawings Figure 1 is a sectional view of a rotary indexing table according to the present invention, utilising a fluid pressure preloaded ball bearing to support the table top plate.

Figure 2 is an enlarged fragmentary view of portions of certain components of the rotary index table as shown in Figure 1 depicted in the locked position, with an exaggerated representation of the bear-race clearances.

Figure 3 is an enlarged fragmentary view of certain of the table components shown in Figure 2 in the unlocked position with an exaggerated representation of the bearing race and balls.

Figure 4 is an enlarged fragmentary view of the components shown in Figures 2 and 3 with the table top removed and a diagrammatic representation of the machining of the upper surfaces.

Figure 5 is a partially sectional view and another form of rotary index table employing the fluid pressure preloaded bearing arrangement according to the present invention.

Detailed description of the preferred embodiment In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 U.S.C. 112. It is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims.

According to the drawings and particularly Figure 1, this view illustrates an embodiment of the invention applied to a rotary indexing table 10 of the same general arrangement as that described in copending Serial Number 244,589, filed April 17, 1981. A complete description of all of the details of the table 10 will not be herein included, but only those details necessary for a complete understanding of the present invention.

The table 10 includes a top plate assembly 12 mounted for rotation on a table base 16. It will be noted that as the interior of the base 10 is sealed by the provision of O-ring gaskets and wiper seals as shown sealing each of the mating components assembled together.

This version ofthetable 10 is usable in either horizontal or vertical orientations of the table, and is shown in Figure 1 in the vertical position with the rotary table top plate 14 having its upper or outer surface 14 oriented in the vertical position. The table top plate 14 is mounted for rotation about the centreline "X" on a machine table base generally indicated as 16, so as to present various aspects of the work pieces mounted to the outer surface to machine tools, engaging elements, etc., suitable fixturing (not shown) mounted to threaded mounting holes 18 being employed for this purpose.

The table top assembly 12 includes the aforementioned top plate 14 which in turn is mounted to a rotating serrated tooth compiling plate 22 by means of a series of cap screws 24 and suitable keys 26 secured by machine screws 28, providing a precise angular indication there between. A cover plate 13 covers a central opening through the top plate 14, with cap screws 17 securing the same.

The rotating serrated tooth plate 22, in turn, is supported by means of a ball bearing assembly 30 including a series of bearing balls 32 disposed in corresponding raceways, 34, 36. Raceway 34 is machined into the outer circumference of the rotating serrated tooth plate 22 and raceway 36 is machined in the interior bore formed in a fixed coupling serrated tooth ring 38 and provides radial and axial support for the table assembly 12 for rotation on the table base 16.

The fixed serrated tooth ring 38 is fixed to the base casting 40 by means of a series of cap screws 42.

The rotating serrated tooth ring 22, in turn, is affixed to a drive tube 44 by means of cap screws 46 and precision keys 48 ensuring rigid precisely located angular orientation there between. The drive tube 44 is adapted to be turned by means of a worm gear 50 affixed to a flange 52 of the drive tube 44 and by means of cap screws 54 and a precision key 56 secured by machine screws 57. The worm gear 50 in turn is adapted to be driven by a gear 58 mounted within the machine cavity and driven by an electric motor gear drive assembly (not shown). In similar fashion to that which is shown and described in Serial Number 244,589, a spur gear series and D.C.

drive motor, when energised, causes rotation of the table top assembly 12.

The worm gear 50 is piloted on a closure plug 50 received within a bore 62 formed in the base casing 40 secured by means of cap screws 63 having a pilot section 64 upon which is rotatably received the worm gear 50 with a bore 66 formed therein slidably fit over the pilot section 64.

A position feedback signal may be provided electronically by means of a encoded assembly indicated at 68 which includes a coupling rotated by the flat of the rotating serrated tooth plate 22 by means of a connection and cap screws 72, a coupling shaft 74 and decoder 76.

As described, the table top assembly 12 is indexable to be precisely located in the locked discrete rotary positions by means of a Hirth coupling arrangement which includes an axially movable piston member 78 which is slidably received on the outside diameter of the drive tube 44 as shown. The piston member 78 is formed with two series of concentric circular rows or rings of serrated teeth on one axial face, outer ring of serrated teeth 80 and inner ring of serrated teeth 82, inner serrated tooth ring 82 adapted to be meshed with the corresponding ring of serrated teeth 84 machined into the interior or undersurface of the rotating serrated tooth plate 22, while serrated teeth 80 are adapted to be meshed with the corresponding ring of serrated teeth 86 on the undersurface or interior of the fixed serrated tooth ring 38.

As described in greater detail in the aforementioned copending patent application 244,589, filed April 1981,this arrangement can provide an enormous number of accurate, repeatable, discrete indexed positions by having a different number of teeth in the inner ring of serrated teeth 82,84 as compared to the outer ring of serrated teeth 80, 86.

For example, the inner serrated teeth 82, 84 may comprise 576 mating teeth, while the outer ring of serrated teeth 80 and 86 may include 625 teeth which gives a total number of discrete positions equal to 360,000.

This indexing requires a rotation of the piston member 78, as well as the table top assembly 12. To achieve this potentially large number of indexed positions, the piston 78 must also be rotatable through 360 .

In the arrangement shown in Figure 1, the gear ring 88 is affixed to the outside diameter of a reduced diameter pilot section 90 of the piston 78 secured together by means of cap screw series 92 located by means of dowels 94. Gear ring 88 includes an outer series of gear teeth 96 in mesh with a drive gear 98 rotatably mounted within the base casting 40.

The drive gear 98 is mounted on a drive shaft 100 with a reduced diameter end 102 supported in suitable bearings 104, the opposite end of the drive shaft 100 being mounted in bearings 106. Bearings 106 in turn are received in a closure plug 108 mounted by means of cap screws 110 to the base casting 40, a suitable closure seal 112 being provided.

The interior opening 114 is machined into the base casting 40 to receive the drive shaft 100 and other components and a suiable plug and opening 116 for introducing suitable lubricant into the space is provided and a breather vent 118 is also provided to enable the addition of lubricant.

The drive shaft 100 is adapted to be rotated by a suitable gear drive assembly 120 in mesh with a worm gear 122 which in turn is driven by a suitable gear train and drive motor (not shown) in similar fashion to the arrangement shown in Serial Number 244,589. The gear 120 is secured by means of a key 124, with a thrust bearing 126 being provided.

In order to absorb the thrusting loads during rotation of the piston 78, a suitable thrust roller bearing 128 is provided positioned against the end face of the gear ring 88 as shown with a wear plate 130 being positioned against a shoulder 132 machined in the base casting 40. Suitable openings 134, 136 are provided to enable communication there through of hydraulic fluids which are introduced in order to provide the actuation of the piston member 78 as will be described.

Piston member 78 is adapted to be axially advanced to bring the serrated teeth 80, 82 into engagement with the serrated teeth 86, 84 by fluid pressure means which includes an hydraulic circuit 138 which includes suitable regulators and valving (not shown) such as to control the application of the hydraulic fluid pressure via a passage shown at 140 into the cavity 142, defined by the end face of piston 78, the interior of the bore 141 in fixed casting 40 receiving the piston 78 and the interior face of the flange 52 of the drive tube 44. Suitable seals are provided including seal 144 extending between the periphery of the gear ring 88 and the interior of the mating bore 141. The piston 78 is received onto the exterior of drive tube 44 a seal 146 disposed there between.A seal 148 extends about the periphery of the flange 52 and sealingly engaging the bore 149 formed in the base casting 40.

Upon actuation of the controls and the introduction of hydraulic pressure into the cavity 142, the table assembly 12 is forced to the left as shown in Figure 1 or downwardly in the horizontal position while the piston 78 is forced to the right tending to move the serrated teeth 80 and 82 into meshing engagement with the serrated tooth rings 84 and 86 respectively while in the locked up or index position.

The area subjected to hydraulic pressure on the drive tube flange 52 is less than the area of the bottom of the piston 78 including the gear ring 88.

There is thus a net upward force generated ensuring tha after the serrated teeth 82,84 are brought into mesh, the serrated teeth 80 are forced upwardly orto the right as shown in Figure 1 into engagement with the serrated teeth 86.

In order to provide disengagement of the serrated teeth 82 and 84 and 80 and 86, there is provided means for generating a fluid pressure force acting to axially move the piston member 78 to disengage the serrated tooth Hirth coupling, which includes a pneumatic circuit 150 including suitable regulator, filter, etc., to produce a controlled air pressure into the passage 152 in communication with a cavity 154, intermediate the end face of the piston 78 and the serrated tooth plate 22. Suitable seal 156 is mounted about the outside diameter of the piston 78, and seal 158 about the interior of the periphery of the bore 159 formed in the piston 78. A seal 160 is mounted intermediate the rotating serrated tooth plate 22 and the fixed serrated tooth ring 38 to complete the sealing of cavity 154.

The O-ring seals 162 and 164 are provided at the interfaces between the fixed serrated tooth ring 38 and the drive tube 44 and rotating serrated tooth plate 22 to further ensure no leakage of air pressure will occur from cavity 154.

The pneumatic circuit 150 applies a constant air pressure in the cavity 154 acting to separate the serrated teeth 80,86 and 82, 84 axially moving the piston 78 to the left as shown in Figure 1, or downwardly in the vertical horizontal mounting of the table.

The hydraulic pressure introduced into the cavity 142 is much higher i.e. on the order of 1000 psi, the pneumatic pressure which is introduced in the regulator pressure being preferably between 40 and 60 psi, the indication of hydraulic pressure in the cavity 142 simply overcomes the pneumatic pressure existing in the cavity 154 to best produce a controlled engagement and disengagement of piston 78 and the Hirth coupling teeth 82, 84, 80 and 86.

According to the concept of the present invention, the ball bearing 30 is provided with a predetermined degree of play of looseness, both radially and axially, such that as the piston 78 is stroked into locked position with the Hirth coupling teeth engaged, ball bearing 30 does not constrain the position of the serrated tooth plate 22 either radially or axially during the full seating of the Hirth coupling teeth. This is shown in exaggerated fashion in Figure 2, the piston 78 shown in a locked position with serrated gear teeth 80,86, and 82,84 in full engagement. In this position clearance still exists between the grooves 36 and 34 and balls 32 as shown in exaggerated fashion in Figure 2.

Also, in this position the undersurface 166 of the table top plate 14 is located against the upper or outer surface 168 such that the fixed serrated tooth ring 38 affords maximum rigidity of the table top plate 14 in the locked position for resisting heavy machining loads such as in broaching operations.

This serves to reinforce the rigidity afforded by the Hirth gear teeth themselves.

Upon release of the hydraulic pressure, the air pressure acting in the cavity 154 again is exerted on the table top assembly 12 causing lifting or axial movement to the right as shown in Figure 3. This has two very significant effects.

Firstly, the clearance in the bearing 30 is taken up by upward movement of the rotating serrated tooth plate 22 until the bearing 30 is loaded to cause a preloading of the bearing 30 and elimination of all the excess clearance as shown in exaggerated form in Figure 3. The movement sufficient to take up the play in the bearing 30 also causes the opening of a gap between the undersurface 166 of the table top plate 14 and the upper surface 168 of the first serrated tooth ring 38.

This enables the indexing rotation of the table assembly 12 with the serrated teeth 80,82 and 84,86 disengaged as shown while avoiding wear which would normally result if the surfaces 166, 168 were left in engagement during indexing rotation.

At the same time, the preloading of the bearing 30 with the table in its rotary or unlocked position enables a relatively precision rotation of the table top assembly 12 such as could be employed during contouring or machining operations requiring continuous rotation of the table top without necessitat ing precision bearings or, encountering the difficulties in achieving reliable full seating of the Hirth coupling teeth 80,86,82,84.

The table is thus usable for both of these purposes.

It is important that the surfaces 166 and 168 be parallel and in engagement with the Hirth coupling in a locked up condition. It is also important that the upper surface 15 of the table top plate 14 be in close parallelism with the plane generated by the Hirth coupling teeth in the various indexed positions. This parallelism is achieved during manufacture of the table by the hydraulic circuit 138 actuating piston 78 such as to cause engagement of coupling serrated teeth 82,84,80,86, successive index positions to locate the plane by a suitable engaging of the upper surface 23 of the gear plate 22.These surfaces are ground as by grinding wheel 170 causing the surface 168 and surface 23 of the rotating serrated tooth plate 22 to be formed parallel to the coupling plane, and even also flush with each other such to provide support of the under surface 166 of the table top plate in the locked positions.

Thus, upon reinstallation of the table top plate 14 the upper surface 15 of the table top plate 14 is also in parallel with the surfaces 166 and 168 and with the plane generated by the Hirth coupling is created. It can be seen that the necessary precision is be achieved relatively simply without requring a high degree of precision of the mating components.

Referring to Figure 5, a fluid pressure bearing preloading arrangement according to the concept of the present invention is provided in a different concept for a rotary table 174 which includes a table top assembly 176 including a top plate 178 having an uppersurface 180 adapted to have a parttobe rotated mounted thereto.

The table top plate 178 of the rotary table 174 in this embodiment in Figure 5 is capable of horizontal orientation only.

The table top plate 178 is secured to a rotating tooth ring 182 by means of a cap screw series 184 in a precision key way 186 adhered by machine screw 188. Serrated tooth ring 182 is provided with seals 190, 192 acting on the periphery of rotating serrated tooth plate 182 and the interior bore 194 and a fixed serrated tooth ring 196 located in alignment therewith and concentric to the gear plate 182. The fixed serrated tooth ring 196 in turn is secured with cap screws 198 and doweling 200 to a base casting 202 to provide relative fixing of the serrated tooth ring 196 with respect to the rotating serrated tooth plate 182. Wiper seals 190, 192 prevent the escape of air pressure from an internal cavity as will be described.

A suitable gasket 204 provided between the table top plate 178 and the rotating serrated tooth plate 182. A gasket 206 is provided between coupling tooth ring 196 and a shoulder 208 mounted in the base casting 202.

The rotating serrated tooth plate 182 is connected to a drive tube 210 by means of cap screws 212 and accurately located by means of a precision key 214 secured by machine screws 216, with seal 218 sealing the interface.

Drive tube 210 is adapted to be rotated to thereby rotate the table top assembly 176 by means of a drive gear 220 secured thereto by means of cap screws 222 and key 224 secured with machine screws 226. The drive gear 220 in turn is adapted to be rotated by means of a drive assembly including the drive gear 228 and drive motor (not shown).

Vent passage 230 is provided to the opening housing drive gear 228 with a vent plug 236 being provided. A fill passage 234 is provided with a plug 232 also provided which is in communication with a cross passage 238, having a plut 240, empties into vent passage 230 to enable lubricant to be added. A suitable drain passage 242, plug 244, cross passage 246 and plug 248 are also provided to enable the lubricant to be drained therefrom.

An axially movable piston member 250 is also provided having inner and outer rings of Hirth serrated teeth 252 and 254 respectively, which mate with a corresponding ring of serrated teeth 256 formed on the undersurface of the rotating serrated tooth plate 182 and a ring of serrated teeth 258 formed on the undersurface of the fixed serrated tooth ring 196. The piston 250 is adapted to be axially moved in so as to move the serrated teeth into and out of engagement.

It is moved into engagement by the application of hydraulic pressure into the cavity 260 intermediate the flange portion 262 of the drive tube 210 and the under or back surface of piston 25. The piston 250 is slidably conceived over an outside diameter 264, the drive tube 210 at the bore 266 formed for this purpose. The cavity 260 is sealed by means of a seal 268 and seal 270, and O-ring seal 272 such as to enable rotation of the drive tube 210 and axial movement of the piston 250.

In this embodiment, the piston 250 is not rotated and this affords fewer indexed positions, which may be adequate for the purpose for which the table is to be employed. Thus, the piston 250 is adapted to be axially movable only, but is connected to rotate with the drive tube 210 and rotating serrated tooth plate 182. For this purpose plug 274 is provided disposed in the bore 276 machined into the upper face of the piston 250 and having a flat sided portion 278 extending into a corresponding machined opening 280 formed in the rotating serrated tooth plate 182.

Hydraulic pressure is introduced in the cross passage 284 and received via a suitable hydraulic circuit 286 indicated diagramatically. A proximity sensor 288 may be provided for determining the zero position thereof, as disclosed in the above referenced serial number 149,906 of May 15, 1980.

Upon introduction of hydraulic pressure into the cavity 260, the piston 250 is axially stroked upwardly as shown in Figure 5 to bring the Hirth coupling into engagement and lock the table in position. To disengage air pressure is introduced into a cavity 290 intermediate the under surface of the rotating serrated tooth plate 182 and the upper face of the piston 250 with the seal 206, wiper seals 192, 190 and seal 218 sealing off this cavity. The air pressure is introduced via cross passage 292 supplied from a pneumatic circuit 294 of a suitable design which may include such conventional components as a filter, regulator, safety switching, etc.Air pressure is continuously applied in the cavity 290, such that upon relief of the relating hydraulic pressure in the cavity 260, the Hirth coupling is immediately separated by withdrawal of the piston 250 under the influence of the air pressure in cavity 290.

The rotary table top assembly 176 is rotatably supported on the base casting 202 by means of "TURCITE" (trademark) bearing rings 296 which are interposed between the under surface 298 of the top plate 178 and the upper surface 300 of the base casting 202 to provide the rotatable support necessary carrying the weight of the table top assembly 176 and enabling rotation of the table by driving of the drive tube 210. In this embodiment, the table is adapted to be urged downwardly as in Figure 5, by the application of fluid pressure in the cavity 290.

This is achieved by the back surface 302 of the piston 250 engaging a front surface 304 of a flange 262, causing a downward force to be exerted on the table assembly 176 upon application of fluid pressure in the cavity 290, to thus preload the "TURCITE" bearings 296.

To enable a proper loading applied to these "TURCITE" bearings 296, the regulation of the air pressure may easily provide the correct amount of preload pressure.

It can be appreciated that the fluid pressure engagement arrangement has been employed in these embodiments to achieve very significant improvements to both of these embodiments without involving major additional structure or complexity.

Many variations of these specifics are of course possible.

Claims (12)

1. In a rotary index table of the type including a table base, a table top assembly rotatably mounted on said base, bearing means rotatably supporting said table top assembly on said base, and means for rotating said table on said rotary bearings, the improvement comprising: fluid pressure means acting on said table top assembly to preload said rotary bearing means.

2. The rotary index table, according to Claim 1, including a Hirth coupling means acting to provide indexed positions of said table top assembly in discrete rotated positions, with said Hirth coupling means including a ring of serrated teeth carried by said table top assembly and an axially movable piston member mounted within said table base, said axially movable piston member being formed with a corresponding ring of serrated teeth adapted to be brought into meshing engagement with said serrated teeth carried by said table top assembly upon axial movement of said axially movable member toward said table top assembly serrated teeth, and means for moving said axially movable piston member to cause engagment and disengagement of said serrated teeth.

3. A rotary table according to Claim 2 wherein said bearing means comprises ball bearing means including a series of balls disposed in corresponding grooves, one of said grooves being mounted to said table base, the other of said grooves being mounted to said table top assembly and wherein said ball bearing is provided with a predetermined amount of play, to enable full seating of said serrated teeth prior to seating of said bearing balls on said grooves, and said fluid pressure means preloading said ball bearings upon activating said fluid pressure means, so as to cause such bearing preloading only with said serrated teeth disengaged.

4. The rotary table according to Claim 3, wherein said fluid pressure means causing said bearing means preloading includes means for causing fluid pressure to be exerted on said axially movable member in a direction tending to disengage said serrated teeth on said axially movable member and said table top assembly respectively whereby said fluid pressure means causes disengagement thereof and preloading of said ball bearing means.

5. The rotary table according to Claim 4 wherein said top plate assembly includes the top plate with an under surface formed thereon and a surface formed on said table base, said surfaces overlying each other with said bearing preload means deactivated and said serrated teeth in engagement and wherein said play in said ball bearing means is sufficient upon activation of said bearing preload means to lift said table top assembly away from said surface on said table base.

6. A rotary table according to Claim 4 wherein said fluid pressure means is constantly applied to act on said axially movable piston member and wherein said means for moving said axially movable piston member includes fluid pressure means acting on said axially movable piston member selectively operable to cause said axially movable piston memberto move to engage said serrated teeth including means for counteracting the effect of said fluid pressure acting on the other of said one side of said axially movable piston member tending to cause disengagement thereof so that said fluid pressure preloading of said ball bearing means is overcome upon actuation of said fluid pressure means to cause engaging movement of said axially movable piston member.

7. The rotary table according to Claim 6, wherein said axially movable piston member comprises a generally annular piston, and wherein said rotary table top assembly includes a drive tube, and wherein said piston is slidably mounted thereon; and wherein said drive tube further includes a flange portion located on said other side of said annular piston; said fluid pressure actuation means includes means defining a fluid pressure cavity defined by a surface of said flange adjacent said annular piston, a surface of said piston, and bore walls formed in said table base whereby upon actuation of said fluid pressure means causing pressurization of said cavity, said table top assembly is biased in the direction to cause said preloading by said fluid pressure means, and said annular piston is urged into engagement with said serrated teeth.

8. The rotary table according to Claim 7, wherein said Hirth coupling further includes a second outer ring of serrated teeth and a second corresponding ring of serrated teeth affixed to said rotary table base and adapted to be brought into engagement with said corresponding teeth upon actuating said annular piston, and wherein said area of said drive tube flange subject to said fluid pressure in said actuation cavity is of lesser area than said area of said annular piston subjected to said fluid pressure and said annular piston is urged into engagement with said teeth carried by said table base after engagement of said gear teeth carried by said annular piston and said table top assembly.

9. The rotary table according to Claim 1, wherein said table top assembly is supported on "TURCITE" bearings and wherein said fluid pressure bearing preloading means merges said table top assembly downwardly into engagement with said "TURCITE" bearings to achieve said bearing preload.

10. The rotary table according to Claim 9, wherein said table top assembly includes a flange member abutted by said axially movable member on the opposite side thereof, upon which there is exerted said fluid pressure of said fluid pressure pre-loading means, whereby said table top assembly is drawn out of engagement therewith and preloads said "TURCITE" bearings.

11. The rotary table according to Claim 1, wherein said table top assembly includes a removable top plate having an under surface, and wherein said table further includes a fixed serrated tooth plate member having a surface adapted to abut said under surface of said table top plate and in alignment therewith, said surface and said outer surface being machined at assembly with said Hirth coupling in said locked position.

12. The rotary table according to Claim 11, wherein both of said surfaces are machine parallel to the plane generated by said Hirth coupling by indexing said Hirth coupling, said table top locating said plane parallel thereto and by machining both of said surfaces parallel to said plane.