Abstract:
This invention discloses a chuck apparatus actuated by a fluid including a body, a plurality of master jaws slidably mounted in the body, a fluid driven piston mounted for axial motion relative to the body along an axis, the piston comprising a plurality of bores extending therethrough along bore axes inclined with respect to the axis, and a plurality of shafts, each slidably mounted in one of the plurality of bores and being coupled to one of the master jaws, and wherein axial movement of the piston along the axis causes the plurality of shafts to move and to cause the plurality of master jaws to move therewith.

Description:
FIELD OF THE INVENTION 
     The present invention relates to pneumatic and hydraulic actuated chucks. 
     BACKGROUND OF THE INVENTION 
     Fluid actuated chucks, both pneumatic and hydraulic, are known in the art. U.S. Pat. Nos. 3,770,287, 4,114,909, 4,139,207, 4,147,312, 4,200,301, 4,229,014, 4,317,577, 4,387,906, 4,697,966, 4,771,963, 4,793,053, 4,890,541, 4,946,178, 4,953,877, 4,979,853, 5,030,048, 5,110,146, 5,125,776, 5,127,780, 5,141,370, 5,174,585, 5,237,895, 5,249,815 and 5,259,630 are believed to be representative of the prior art. In general, fluid actuated chucks include a piston which axially drives a centrally located wedge which engages chuck jaws. The axial movement of the wedge causes the jaws to move radially inwards or outwards. 
     One of the problems of prior art fluid actuated chucks is that the jaws are generally not sealed from possible contamination from chips and machining fluids. In certain machining operations, such as grinding, chips can degrade the performance of the chuck. 
     In general, the inner sliding portion of the jaws of prior art fluid actuated chucks has a T-shaped cross section. The plurality of tolerances in machining the sliding portion of the jaws and the corresponding channels in the chuck limits the accuracy and repeatability of the chuck usually to no better than one micron. 
     It is believed that the same plurality of tolerances is the cause of another problem associated with prior art chucks. The problem is that during operation at relatively high rotational speeds, the chuck jaws sometimes have a tendency to “self-open”, that is, to loosen their grip on the workpiece. 
     In a perfectly manufactured chuck, the chuck jaws lie along axes which are coplanar. In actuality, due to the above mentioned tolerances, each chuck jaw does not lie exactly on its corresponding ideal axis. Rather, each end of each chuck jaw lies out of the ideal common plane of the ideal axes. During operation at relatively high rotational speeds, it is believed that relatively large centrifugal forces develop which cause the ends of the chuck jaws to become further displaced from the ideal common plane, thereby causing loosening of the workpiece. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide a novel fluid actuated chuck which has better sealing properties, accuracy and repeatability than prior art fluid actuated chucks. A chuck constructed in accordance with a preferred embodiment of the present invention may have submicron repeatability even when it is made using the same conventional manufacturing techniques used in constructing prior art chucks. 
     In addition, a chuck constructed in accordance with a preferred embodiment of the present invention substantially prevents loosening of a workpiece even during relatively high rotational speeds. 
     There is thus provided in accordance with a preferred embodiment of the present invention a chuck actuated by a fluid including a body, a plurality of master jaws slidably mounted in the body, a fluid driven piston mounted for axial motion relative to the body along an axis, the piston including a plurality of bores extending therethrough along bore axes inclined with respect to the axis, and a plurality of shafts, each slidably mounted in one of the plurality of bores and being coupled to one of the master jaws, and wherein axial movement of the piston along the axis causes the plurality of shafts to move and to cause the plurality of master jaws to move therewith. 
     There is also provided in accordance with a preferred embodiment of the present invention a fluid actuated chuck including a body, a plurality of master jaws mounted for radial motion in a plane with respect to the body, a fluid driven piston mounted for axial motion relative to the body along an axis substantially perpendicular to the plane, the piston comprising a plurality of bores extending therethrough along bore axes inclined with respect to the axis and with respect to the plane, and a plurality of shafts, each slidably mounted in one of the plurality of bores and being coupled to one of the master jaws, and wherein axial movement of the piston along the axis causes the plurality of shafts to move radially relatively to the body and to cause the plurality of master jaws to move radially therewith. 
     In accordance with a preferred embodiment of the present invention, the plurality of bores and the plurality of shafts have corresponding generally circular cross sections. 
     Additionally in accordance with a preferred embodiment of the present invention, each master jaw is mounted for radial motion in a radial jaw bore, the plurality of master jaws and the plurality of radial jaw bores having corresponding generally circular cross sections. Preferably, each radial jaw bore is substantially sealed. 
     Further in accordance with a preferred embodiment of the present invention, the fluid actuated chuck also includes a plurality of seals operative to substantially seal the body, the plurality of master jaws, the piston and the plurality of shafts. 
     Still further in accordance with a preferred embodiment of the present invention, the fluid used to actuate the chuck is operative to lubricate the body, the plurality of master jaws, the piston and the plurality of shafts. 
     In accordance with a preferred embodiment of the present invention, a central shaft is provided for supplying pressurized air or hydraulic fluid to the piston for driving thereof. 
     Additionally in accordance with a preferred embodiment of the present invention, the plurality of master jaws are mounted such that displacement thereof is substantially prevented during operation at relatively high rotational speeds. 
     Further in accordance with a preferred embodiment of the present invention, a plurality of work jaws are fastened to the plurality of master jaws, such that the plurality of work jaws substantially seals the plurality of master jaws. 
     In accordance with a preferred embodiment of the present invention, each work jaw includes a generally axial tongue and each master jaw has a corresponding generally axial slot, such that the tongue fits into the slot. 
     The work jaws may be any shaped jaws such as soft jaws, pie jaws or half round jaws, and may be of different sizes and formed from a variety of materials. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which: 
     FIG. 1 is a front view illustration of a fluid actuated chuck constructed and operative in accordance with a preferred embodiment of the present invention, wherein jaws of the chuck are in a substantially open position; 
     FIG. 2 is a side sectional view of the fluid actuated chuck of FIG. 1, taken along lines II—II in FIG. 1; 
     FIG. 3 is a front view illustration of the fluid actuated chuck of FIG. 1, wherein jaws of the chuck are in a substantially closed position; 
     FIG. 4 is a side sectional view of the fluid actuated chuck of FIG. 3, taken along lines IV—IV in FIG. 3; 
     FIGS. 5A and 5B are simplified pictorial illustrations of accurate positioning of the work jaws with respect to the master jaws, as known in the art; and 
     FIGS. 5C is a simplified pictorial illustration of accurate positioning of the work jaws with respect to the master jaws in accordance with a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to FIGS. 1 and 2 which illustrate respective front and side partially sectional views of a fluid actuated chuck  10  constructed and operative in accordance with a preferred embodiment of the present invention. The chuck  10  preferably is fastened to a machine tool (not shown), such as to a spindle of a lathe or a grinder, or to a table of a milling machine, by means of a flange  11 . The chuck  10  comprises a body  12  which is preferably constructed of an alloy steel. 
     The chuck  10  preferably comprises a plurality of radial jaw bores  14  in each of which is mounted a master jaw  16 . The master jaws  16  are preferably made of an alloy steel. The embodiment illustrated in FIGS. 1 and 2 has three jaw bores  14  and three master jaws  16 , although it is appreciated by persons skilled in the art that other embodiments of the present invention may include a different number of bores and jaws. 
     Each jaw bore  14  and master jaw  16  preferably have corresponding, generally concentric circular cross sections. The jaw bores  14  along with each corresponding master jaw  16  are radially spaced substantially equally from one another. In the illustrated embodiment, the spacing is substantially 120 degrees. 
     Preferably associated with each master jaw  16  is a dynamic seal  18  which substantially seals the interface of the body  12  and each master jaw  16  from contamination. 
     Associated with each master jaw  16  is a radial axis  20  along which the master jaw  16  slides. The plurality of axes  20  of the plurality of master jaws  16  are substantially coplanar and define a plane  22 . 
     The body  12  is provided with an inner race  24  whose central axis  25  is substantially perpendicular to the axis  22 . Slidably mounted in the race  24  is a fluid driven piston  26  which is preferably provided with a plurality of dynamic seals, such as seals  28  and  30 . The race  24  and the piston  26  preferably have corresponding, substantially concentric circular cross sections. Piston  26  is thus substantially concentric with the axis  25 . The piston  26  moves substantially axially relative to the body  12  substantially along the axis  25 . 
     It is important to note that the tolerances achievable in machining the generally circular race  24 , piston  26 , jaw bores  14  and master jaws  16  are generally tighter than the tolerances achievable with prior art chucks. Prior art chuck jaws generally have T-shaped cross sections which inherently have more surfaces to be machined than circular cross sections. An increase in the surfaces which have to be machined means an increase in the total tolerance sum. 
     The piston  26  is preferably driven pneumatically via a fluid central shaft  32 . Alternatively, the piston  26  may be driven hydraulically, typically by means of a remote shaft operatively connected with to a hydraulic power source as is known in the art. 
     The central shaft  32  is preferably attached to the body  12  by means of screws  34 . The operation of the central shaft  32  and the ensuing axial motion of the piston  26  is described hereinbelow. 
     The piston  26  is provided with a plurality of bores  50  extending therethrough along bore axes  52  inclined with respect to the axis  25  and with respect to the plane  22 . Slidably mounted in each bore  50  is a shaft  54  which is preferably provided with a dynamic seal  56 . Each bore  50  and shaft  54  correspond to one of the plurality of master jaws  16 . Each shaft  54  is coupled at an end  57  thereof to a recess  58  in the corresponding master jaw  16 . Each shaft  54  is preferably constructed of tool steel. 
     Preferably associated with each master jaw  16  is a work jaw  60  which is attached to the master jaw  16  preferably by means of screws  62  which are screwed into threaded holes  64  in the master jaw  16 . In order to facilitate engagement of the screws  62  in the master jaw  16 , the master jaw  16  may be formed with a generally flat face  65 , as shown in FIGS. 5A-5C. 
     The work jaws  60  may be any standard jaw of any size known in the art, such as soft jaws, pie jaws, or half circle jaws, and typically may be constructed of an aluminum alloy, mild steel or low alloy steel. 
     The interface between each work jaw  60  and each master jaw  16  is preferably substantially sealed by seals  68 , as shown in FIGS. 2,  4  and  5 A- 5 C. 
     It should be noted that generally the entire perimeter of each master jaw  16  is enveloped by the corresponding jaw bore  14 . The generally flat face  65  does not extend the full axial length of the master jaw  16 . 
     As is known in the art, the work jaw  60  must be positioned accurately with respect to the master jaw  16  before fastening the screws  62 . Reference is now made to FIGS. 5A-5C which illustrate alternative methods of accurately positioning the work jaw  60  with respect to the master jaw  16 . 
     As seen in FIG. 5A, the work jaw  60  may include a plurality of pins  76  which mate with corresponding sockets  78  in the master jaw  16 , as is known in the art. 
     Alternatively, as seen in FIG. 5B, the master jaw  16  may include a pair of generally orthogonal tongues  80  which mate with corresponding slots  82  in the work jaw  60 , as is known in the art. The arrangement illustrated in FIG. 5B is typically more accurate than the arrangement shown in FIG.  5 A. 
     Reference is now made to FIG. 5C which illustrates a further alternative method of accurately positioning the work jaw  60  with respect to the master jaw  16  in accordance with a preferred embodiment of the present invention. The work jaw  60  comprises a generally axial tongue  90  which fits into a corresponding generally axial slot  92  in the master jaw  16 . This arrangement has been found to be as accurate as the arrangement of FIG.  5 B and is easier to machine. 
     The clamping action of the chuck  10  is now described with reference to FIGS. 1 and 2. The chuck  10  is illustrated in FIGS. 1 and 2 in a substantially open configuration. A workpiece (not shown) is centrally inserted between ends  66  of the work jaws  60 . The workpiece is then clamped by moving the master jaws  16  and the work jaws  60  radially inwards thereagainst as described hereinbelow. 
     In order to move the master jaws  16  and the work jaws  60  radially inwards, the piston  26  is driven backwards in the direction of arrow  38 , shown in FIG. 2, by the action of a fluid entering an inlet port  39  of the central shaft  32 , passing through an elongate channel  40  of the central shaft  32  and entering a cavity  41  formed between a front face  42  of the piston  26  and a rear face  43  of the body  12 . 
     The fluid pressure in the cavity  41  pushes against the face  42  of the piston  26  and thereby causes the piston  26  to move backwards along the axis  25  in the direction of arrow  38 . Since each axis  52  of each shaft  54  is inclined with respect to the axis  25 , the axial movement of the piston  26  in the direction of arrow  38  causes each shaft  54  to slide radially inwards. 
     Since the end  57  of each shaft  54  is coupled to the corresponding master jaw  16 , which is in turn fastened to the corresponding work jaw  60  by means of the screws  62 , the radially inward motion of the shafts  54  causes the master jaws  16  and the work jaws  60  to move radially inwards, as shown in FIGS. 3 and 4. The work jaws  60  thus move radially inwards and clamp the workpiece (not shown). 
     Typically the diametral movement of the master jaws  16  and the work jaws  60  is 1-3 mm, as is known in the art. 
     Release of the workpiece is now described with reference to FIGS. 3 and 4. 
     In order to move the master jaws  16  and the work jaws  60  radially outwards, the piston  26  is driven forwards in the direction of arrow  44 , opposite to the direction of arrow  38  shown in FIG. 2, by the action of fluid entering the inlet port  39 , passing through a rear channel  46  of the central shaft  32  and pushing against a rear face  48  of the piston  26  in the direction of arrow  44 , thereby causing the piston  26  to move forwards along the axis  25  in the direction of arrow  44 . 
     Since each axis  52  of each shaft  54  is inclined with respect to the axis  25 , the axial movement of the piston  26  in the direction of the arrow  44  causes each shaft  54  to slide radially outwards. The radially outward motion of the shafts  54  causes the master jaws  16  and the work jaws  60  to move radially outwards, thereby releasing the workpiece (not shown). 
     Conventional valve devices known in the art are used to direct the flow of fluid either to channel  40  or to channel  46 . 
     It is appreciated from the foregoing description that the fluid which actuates the chuck  10  also serves to lubricate the body  12 , the plurality of master jaws  16 , the piston  26  and the plurality of shafts  52 . Optionally associated with each master jaw is a lubrication hole  70 , shown in FIGS. 2 and 4, although in a preferred embodiment of the present invention the chuck  10  is adequately lubricated even without holes  70 . 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention is defined only by the claims that follow.