Air shaft
FIELD OF THE INVENTION 
     This invention relates to expansible shafts. 
     BACKGROUND OF THE INVENTION 
     There are available a number of fluid operated, expansible shafts. In most, buttons in the periphery of the shaft are forced radially outward into engagement with a surrounding core when fluid under pressure is supplied to the shaft interior. These devices are subject to several problems, including loss of holding force due to leakage, clogging caused by fiber particles and other foreign materials, and inability without expensive couplings to add make-up air under leakage conditions. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an expansible shaft in which the problems of fluid leakage failure are eliminated. The core-engaging buttons are driven outwardly by a spring loaded cam, fluid under pressure is used to retract rather than to expand them, and any possible leakage will occur only when the shaft is stationary. In preferred embodiments, dirt and debris clogging is prevented by a flat circular spring that both seals the annulus between each button and the shaft periphery and retracts the buttons radially inwardly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drawings show the preferred embodiment, which is then described. In the drawings: 
     FIG. 1 is a perspective view of the shaft of the preferred embodiment with the buttons fully expanded; 
     FIG. 2 is a perspective view of internal parts of the shaft of FIG. 1; 
     FIG. 3 is a longitudinal cross-section of the shaft of FIG. 1 with the buttons retracted; 
     FIG. 4 is a longitudinal cross-section of portions of the shaft of FIG. 1 with the buttons expanded in contact with a core; 
     FIG. 5 is a sectional view taken at 5--5 of FIG. 4; and, 
     FIG. 6 is a sectional view of portions of the preferred embodiment. 
    
    
     Referring now to the drawings, expansible shaft 10 includes a hollow cylindrical body 12 in which is mounted a co-axial, axially movable operating rod 14. In the embodiment shown, shaft 10 has two axially-spaced button sections 16 and two piston sections 18, a mounting arbor 20 at the end of the shaft adjacent piston sections 18, and an end plate 22 at the end adjacent button sections 16. 
     Each of button sections 16 includes four buttons 24, spaced at 90° intervals around and projecting through respective holes 26 in the cylindrical wall of body 12, a cam 28 on rod 14, a stop 30, and a spring 32 between stop 30 and cam 28 and urging the two apart. A stop washer 34 on, and snap ring 36 attached to, rod 14 limit the axial movement of cam 28 away from stop 30. Cam 28 includes a central axial bearing 38 forming a close slip fit with rod 14 and a cylindrical recess 40 at the end thereof facing stop 30 receiving an end of spring 32. The exterior of the cam is circular in transverse cross-section and defines both cylindrical and truncated conical caming surfaces, 42 and 44 respectively. The slope of conical surface 44 is 1:4. Stop 30 is a cylindrical disc having a central hole forming a loose slip fit with rod 14 and an outer periphery forming a similar fit with the interior cylindrical wall 11 of body 12. Spring 32 comprises a series stack of belleville spring washers 45 (see FIG. 6). Four circumferentially-spaced cap screws 48 extend radially through the wall of body 12 and engage the side of stop 30 opposite spring 32, thus preventing the stop from moving axially away from cam 28. 
     Each button 24 is circular in cross-section and has an inner portion 51 of major diameter forming a slip fit with hole 26, an outer portion 52 of reduced diameter and an annular step 54 between the two. A ball 50 is mounted in a socket at the radially inner end of inner portion 51. A combination spring-seal 56 fits in a counterbore 58 at the outer end of hole 26 and is held in place by a snap ring 60 in groove 59. Spring-seal 56 includes inner and outer steel rings, which form close fits with, respectively, counterbore 58 of hole 26 and reduced diameter portion 52 of button 24, bonded together by an intermediate ring of urethane or a similar elastomeric material. 
     Each piston section 18 includes a piston 62 fixed on rod 14 by a set screw 57, an annular piston stop 64, and a seal plate 66. O-Rings 68 in recesses in the inner and outer peripheries of pistons 62 and seal plate 66 form seals with rod 14 and the inner surface 11 of body 12. The side of piston 62 facing seal plate 66 is flat; the opposite side defines a stepped cylinder of reduced diameter sized to fit into the center hole 72 of stop 64. A counterbore 70 is provided in the face of seal plate 66 facing piston 62. Stop 64 and seal plate 66 are restrained against axial movement away from piston 60 by respective sets of radially-inwardly projecting cap screws 48 which engage the sides of the stop and seal plate opposite piston 62. 
     Other sets of cap screws 49 hold end plate 22 and mandrel 20 in place. 
     Rod 14 includes an air bore 78 extending axially therethrough, and intersecting bores 74 extending radially from central bore 78 to within the recess 70 of a respective one of seal plates 66. The end of air bore 78 at end plate 22 is plugged. Flexible hose 80 connects the other end of air bore 78 to an air bore 82 through mandrel 20, and an air valve 76 is threaded into the free end of mounting mandrel 20. 
     As will be evident, rod 14 is axially movable within and relative to body 12, and the amount of axial movement is limited by the distance between the stops 64 and seal plates 66 of piston sections 18. At one extreme (in which buttons 24 are fully retracted, substantially as shown in FIG. 3) the left end of piston 62 fits within central bore 72 of stop 64 and axially-facing annular piston face 61 engages the facing end surface 65 of stop 64. At the other extreme (in which buttons 24 are fully extended, slightly beyond the position shown in FIG. 4) the opposite end 63 of piston 62 engages the annular surface 37 of seal plate 66 surrounding recess 70. Each cam 28 has an axial length slightly greater than the permitted axial travel of rod 14. The cams are positioned on the rod so that buttons 24 will engage the minimum diameter end of the conical cam surface 44 of the respective cam 28 when rod 14 is in the button-retracted position, and the other end of cam 28 (e.g., the far end of the cylindrical cam surface 42) when rod 14 has moved to the button-extended position. Springs 32 bias rod 14 towards the button-extended position; and spring-seals 56 hold buttons 24 against their respective cams. 
     The number of belleville washers 46 in each spring 32, and the configuration of each washer, is such that the force exerted by the spring remains substantially constant as rod 14 moves between its two extreme positions. In practice, washers having an h/t ratio (t being the thickness of the material of the washer and h being the free height of the washer less its thickness) in the range of 1.2 to 1.7 (typically 1.41) are used, and the total number of washers is such that each washer is almost flat when the rod is in the extreme button-retracted position, and in the button-extended position the deflection of each washer will be not less than about 1/2 h. 
     In use, shop air is connected to air valve 76 causing air under pressure to flow, through bores 82, 74, 78, into recesses 70 between pistons 60 and seal plates 66, forcing the pistons away from the seal plates and moving rod 14 to the left (as shown). Stops 36 engage the right (as shown) ends of cams 28 and pull the cams to the left, against the force of springs 32. Pistons 62 continue to move away from plates 66 until, as shown in FIG. 3, piston face 61 engages stop 64. In this position, balls 50 of buttons 24 are aligned with the minimum diameter ends of cams 28 and seal-springs 56 force the buttons radially inwardly until their outer ends are flush with, or slightly within, the outer cylindrical surface of body 12. Shaft 10 may now be inserted into a core 100 (FIGS. 4 and 5). 
     When the shaft is in position within the core, the supply of pressurized air is disconnected, valve 78 is relieved, the pressure in the piston section 18 drops to atmospheric, and springs 32 push cams 28 away from stops 30, to the right as shown. As the cams move, buttons 24 ride up conical cam surfaces 44 and are forced radially outwardly. Cams 28 continue to move axially, forcing buttons 24 radially, until the buttons tightly engage the inside of core 100. If the size of the core permits, buttons 24 will be forced outwardly to their fully extended configuration (with balls 50 engaging cylindrical cam surfaces 42) and rod 14 and cam 28 will continue to advance axially until the flat surfaces 63 of pistons 62 come into engagement with surfaces 67 of seal plates 66. 
     OTHER EMBODIMENTS 
     In other embodiments, the structure, i.e., mandrel 20 and end plate 22, at opposite ends of body 12 may be varied as required depending on the type of support or other machinery with which the expansible shaft is to be used. Similarly, different shafts will include different numbers of button sections 16 and piston sections 18, and springs 32 may be of different types and form. Typically, the number of button sections 16 will depend on the particular core, roll, etc. to be supported; the springs of each will provide the force needed to insure the buttons positively engage the core; and sufficient piston sections 18 will be provided to retract the springs of whatever button sections are present. 
     These and other embodiments will be within the scope of the following claims: