Abstract:
A workholding apparatus including a body and a drive member carried by the body, so that the drive member and body partially define a fluid chamber therebetween for containing a fluid. A driven member is also carried by the body and includes multiple displacement reliefs therein. An intermediate member with a displacement relief is received between the drive and driven members. The intermediate member prevents the drive member from extruding through the displacement reliefs in the driven member under fluid pressures of the fluid, thereby enabling use of the apparatus under higher performance applications that would not be possible without the intermediate member.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to machine tools and more particularly to hydrostatic workpiece holders.  
         BACKGROUND OF THE INVENTION  
         [0002]    Various hydrostatic workpiece holders are known, such as that disclosed in U.S. Pat. No. 6,015,154, which has one or more chambers containing a fluid which, when pressurized, displace one or more polymeric rings which in turn displace one or more metal sleeves into engagement with a workpiece. While this hydrostatic tool holder is effective and reliable under most conditions, the performance and durability can be improved upon for high performance applications.  
         SUMMARY OF THE INVENTION  
         [0003]    In some high performance applications, a more robust workpiece holder is required because the polymeric rings may become displaced beyond their elastic limits and extrude through portions of the metal sleeves.  
           [0004]    A workholding apparatus includes a body and a drive member carried by the body, so that the drive member and body partially define a fluid chamber therebetween for containing a fluid. A driven member is likewise carried by the body, and includes a displacement relief therein. An intermediate member is interposed between the drive and driven members. The drive, driven, and intermediate members are relatively lapped with respect to one another. Accordingly, the intermediate member prevents the drive member from extruding through the displacement relief in the driven member under fluid pressures of the fluid.  
           [0005]    In one embodiment, the driven member is disposed about the exterior of an arbor body with the intermediate member, drive member, and associated fluid chamber defined within the driven member and arbor body so that the force of the pressurized fluid in the fluid chamber acts radially outwardly on the driven member to displace or expand the driven member into engagement with the inner surface of a workpiece. In another embodiment, the driven member is received within a bore of a chuck body with the intermediate member, drive member, and associated fluid chamber disposed about the driven member so that the force of the pressurized fluid in the fluid chamber acts radially inwardly on the driven member to displace or contract the driven member into engagement with a workpiece. In each embodiment, the force of the pressurized fluid is transferred through the intermediate and drive members to displace the driven member.  
           [0006]    Objects, features, and advantages of this invention include providing a workpiece holder which has a driven member that may be significantly displaced under a relatively low pressure of fluid applied to the driven member to firmly hold a workpiece received adjacent to the driven member, has an intermediate member that prevents a drive member from becoming plastically deformed and extruded through portions of the driven member, can handle higher fluid pressures and provide greater holding power, has longer tool life, has a greater expansion or contraction range, can be used to firmly hold and locate workpieces formed of cast material, can conform to a workpiece which is out of round, dampens vibrations during the machining process, provides a better finish of the part machined, repeatably and reliably holds and locates workpieces, reliably centers each workpiece, may be formed of different thicknesses to accommodate different sized parts, can be displaced generally radially inwardly or radially outwardly and is of relatively simple design and economical manufacture and assembly and has a relatively longer useful life in service. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiments and best mode, appended claims, and accompanying drawings in which:  
         [0008]    [0008]FIG. 1 is a cross-sectional view of an arbor embodying the present invention;  
         [0009]    [0009]FIG. 2 is a side view of a collet of the arbor of FIG. 1;  
         [0010]    [0010]FIG. 3 is a side view of a baffle of the arbor of FIG. 1;  
         [0011]    [0011]FIG. 4 is an end view of the baffle of FIG. 3;  
         [0012]    [0012]FIG. 5 is a cross-sectional view of the arbor of FIG. 1 taken along line  5 - 5 ; and  
         [0013]    [0013]FIG. 6 is a cross-sectional view of a chuck embodying the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    Referring in detail to the drawings, FIG. 1 illustrates a hydrostatic workpiece holder, and more specifically, a hydrostatic arbor  10 . The arbor  10  includes a body  12  having a cylindrical shaft or mandrel portion  14  and a radially extending mounting flange portion  16 . The body  12  is constructed to be mounted on a machine tool spindle  18  by suitable cap screws  20  as shown. The body  12  includes a main fluid passage  22  and branch fluid passages  24 ,  26  that are constructed to be filled with a pressurized fluid. As is well known in the art, the main fluid passage  22  is supplied with pressurized fluid from a pump carried by the body  12  or through the machine tool spindle  18  by a remote pump. An external annular recess  28  in a first outer diameter or first outer surface  30  of the mandrel portion  14  of the body  12  partially defines a fluid chamber  32  that is sealed by resilient polymeric rings  34 , such as O-rings, that are disposed within annular grooves  36  in the mandrel portion  14 . The mandrel portion  14  is stepped to include the first outer surface  30  and a larger, second outer diameter or outer surface  31 .  
         [0015]    A circumferentially continuous sleeve or diaphragm  38  is adjacent to and circumscribes the mandrel portion  14  of the body  12  and thereby partially defines the fluid chamber  32 . The diaphragm  38  includes an inner cylindrical surface  40  that cooperates with the first outer surface  30  of the mandrel portion  14  of the body  12  and further includes an oppositely disposed outer cylindrical surface  42 . The diaphragm  36  may be manufactured by injection molding, machined from a solid block, and the like, and may be composed of a polymeric material such as Delrin®, Nylon®, polyurethane, or the like. In any case, the diaphragm  38  is composed of any material that permits radially outward displacement of a mid-section  44  of the diaphragm  38  under the fluid pressure force acting thereon, yet enables the diaphragm  38  to retain surface contact with the polymeric rings  34 .  
         [0016]    A metal sleeve, retainer, or baffle  46  is adjacent to and circumscribes the diaphragm  38 . The baffle  46  includes a diaphragm engaging cylindrical inner surface  48  that cooperates with the outer cylindrical surface  42  of the diaphragm  38  and further includes an oppositely disposed collet engaging surface or outer surface  50 . Alternatively, the baffle  46  may be located within an exterior annular relief (not shown) of the diaphragm  38  such that the baffle  46  and diaphragm  38  share a common outside diameter. Typically, the baffle  46  has a uniform wall thickness of 0.008″ to 0.010″ but may include any other suitable wall thickness for any given arbor design. Referring now to FIGS. 3 and 4, the baffle  46  is a split sleeve with a displacement slot  52  to permit the baffle  46  to expand radially outwardly. The baffle  46  may be rolled from a flat strip of stainless steel, cold rolled steel, aluminum, copper, or the like in order to define the displacement relief as a slot or gap between two ends  54 ,  56  of the rolled strip of material as shown. Alternatively, the baffle  46  may be constructed from tube stock and the displacement slot  52  may be cut therefrom. The displacement slot  52  extends parallel to the longitudinal axis of the baffle  46  and, as shown, is a single gap slot or void. While a single slot  52  is preferred, it is contemplated that multiple circumferentially spaced apart slots could be incorporated for use as displacement reliefs, as is known in the art of collet design. Nonetheless, the baffle  46  is composed of a material and constructed in a manner that permits outward radial displacement thereof.  
         [0017]    Referring again to FIG. 1, a split sleeve or collet  58  is adjacent to and circumscribes the baffle  46 . Accordingly, the collet  58 , baffle  46 , and diaphragm  38  are in a relatively lapped relationship. The collet  58  includes an inner surface  60  that engages the outer surface  50  of the baffle  46  and the second outer surface  31  of the body  12 . The collet  58  further includes an oppositely disposed outer surface  62 . Alternatively, the collet  58  may include an internal annular relief (not shown) for capturing the baffle  46  such that the baffle  46  and collet  58  share a common inside diameter.  
         [0018]    As shown in FIG. 2, the collet  58  is generally tubular or cylindrical and includes a plurality of circumferentially spaced and longitudinally extending through slots or displacement reliefs  66  formed therein such as by milling or electro-discharge machining. The reliefs  66  may be bounded by bearing sections  68  of the collet as shown, or may be formed into the ends  70 ,  72  of the collet  58  as is well known in the art of collet design. The reliefs  66  sufficiently weaken the collet  58  for facilitating radial displacement of at least the bearing sections  68  of the collet  58 . The collet  58  may be composed of a metal such as hardened SAE 4130 or any other suitable metal. Nevertheless, the collet  58  is composed of a material and constructed in a manner to permit outward radial displacement thereof.  
         [0019]    Referring to FIG. 1, a retainer ring  74  is adjacent to and circumscribes the mandrel portion  14  of the body  12  just outboard of the collet  58 . The retainer ring  74  is composed of a metal such as heat treated SAE 6150, but may be composed of any other suitable material. A nose piece  76  circumscribes and caps the mandrel portion  14  of the body  12 . The nose piece  76  is held to the body  12  by cap screws  78  that are threaded into the end of the mandrel portion  14  of the body  12 . A set screw  80  threads into the nose piece  76  to close off the main fluid passage  22 . The nose piece  76  is composed of heat treated SAE 6150, but may be composed of any other suitable material.  
         [0020]    In assembly, the polymeric rings  34  are stretched over the mandrel portion  14  of the body  12  and positioned into the annular grooves  36 , as shown in FIG. 1. The diaphragm  38  is then telescoped or assembled coaxially over the end of the mandrel portion  14  in abutment with a first shoulder  82  of the mandrel portion  14  of the body  12  and in sealing engagement with the resilient polymeric rings  34  to compress the rings  34  and seal the fluid chamber  32 . The baffle  46  is then assembled over the diaphragm  38  and longitudinally centered thereon. The collet  58  is then assembled over the baffle in abutment with a second shoulder  84  of the mandrel portion  14  of the body  12 . Referring now to FIG. 5, the collet  58  is angularly oriented or clocked with respect to the baffle  46  such that the displacement slot  52  in the baffle is clocked between adjacent displacement reliefs  66  in the collet  58 . As shown in FIG. 1, the retainer ring  74  is assembled over the end of the mandrel portion  14  of the body  12 . Finally, the nose piece  76  is assembled over the end of the mandrel portion  14  of the body  12  and abuts the retainer ring  74  as shown. The cap screws  78  are then threaded through the end of the nose piece  76  and into the end of the mandrel portion  14  to secure the assembly together. Accordingly, the mandrel portion  14  of the body  12  carries thereon the various assembled components described above to constitute the arbor  10 .  
         [0021]    In use, a workpiece  100  is disposed over the outer surface  62  of the collet  58  until the workpiece  100  engages the second shoulder  84  of the body  12 . The workpiece  100  may be a cast iron sleeve, a gear blank, or any other workpiece suitable for mounting on an arbor. A cast iron sleeve such as a cylinder liner for an engine has relatively rough surfaces and significant variations in inside and outside diameter. Thus, a relatively large displacement of the collet  58  is required to firmly hold and accurately locate such workpieces on the arbor  10 .  
         [0022]    To firmly hold the workpiece  100  on the arbor  10 , fluid under pressure is provided from an external or internal source through the main fluid passage  22  and branch fluid passages  24 ,  26  and into the fluid chamber  32 . The force of the pressurized fluid radially outwardly displaces the resilient diaphragm  38  which firmly engages and radially outwardly displaces the baffle  46  which, in turn, firmly engages and radially outwardly displaces the collet  58  to urge the collet  58  into firm engagement with an inner surface  102  of the workpiece  100  to firmly hold and accurately locate the workpiece  100  for machining operations to be performed thereon. To remove the workpiece  100  after machining operations, the pressure of the fluid supplied to the fluid chamber  32  is decreased, thereby decreasing the pressure of the fluid in the fluid chamber  32  to thereby relax the diaphragm  38 , baffle  46 , and collet  58 . Thus, the diaphragm  38  acts as a drive member to radially outwardly urge a driven member (collet  58 ) into engagement with the workpiece  100  and the baffle  46  is an intermediate member to prevent the relatively softer diaphragm material from extruding through the reliefs  66  in the collet  58 .  
         [0023]    Referring now to a second embodiment, FIG. 6 illustrates a hydrostatic workpiece holder, and more specifically, a hydrostatic chuck  110 . The chuck  110  is similar to the arbor  10  embodiment of FIGS. 1 through 5 in that it is essentially a female version thereof. Accordingly, for brevity and clarity, some details in common between the two embodiments will be omitted from discussion of the chuck  110 .  
         [0024]    The chuck  110  includes a body  112  having a cylindrical tube or socket portion  114  and a radially extending mounting flange portion  116 . The body  112  is constructed to be bolted to a machine tool spindle (not shown) for co-rotation therewith. The body  112  includes a main fluid passage  122  and branch fluid passages  124 ,  126  that are constructed to be filled with a pressurized fluid. As is well known in the art, the main fluid passage  122  is supplied with pressurized fluid either by a pump carried by the body  112  or through the machine tool spindle (not shown) by a remote pump. The socket portion  114  is stepped to include a first inner diameter or first inner cylindrical surface  130  and a smaller, second inner diameter or inner cylindrical surface  31 . An internal annular recess  128  in the first inner surface  130  partially defines a fluid chamber  132  that is sealed by polymeric rings  134  disposed within annular grooves  136  in sidewalls of the socket portion  114 .  
         [0025]    A sleeve or diaphragm  138  is adjacent to and disposed within the first inner surface  130  of the socket portion  114  of the body  112  and partially defines the fluid chamber  132 . The diaphragm  138  includes an outer cylindrical surface  140  that cooperates with the first inner surface  130  of the mandrel portion  114  of the body  112  and further includes an oppositely disposed inner cylindrical surface  142 . The diaphragm  138  is composed of any material that permits radially outward displacement of a mid-section  144  of the diaphragm  138  under fluid pressure thereon, yet enables the diaphragm  138  to retain surface contact with the polymeric rings  134 .  
         [0026]    A metal sleeve or baffle  146  is adjacent to and disposed within the diaphragm  138 . The baffle  146  includes a diaphragm engaging surface or outer surface  148  that cooperates with the inner cylindrical surface  142  of the diaphragm  138  and further includes an oppositely disposed collet engaging surface or inner surface  150 . Alternatively, the baffle  146  may be located within an exterior annular relief (not shown) of the diaphragm  138  such that the baffle  146  and diaphragm  138  share a common inside diameter. The baffle  146  includes a displacement relief or slot (not shown in FIG. 6, but like that shown previously in FIGS. 3 and 4) to enable the baffle  146  to displace radially inwardly. The baffle  146  is composed of a material and constructed in a manner that permits inward radial displacement thereof.  
         [0027]    A sleeve or collet  158  is adjacent to and disposed within the baffle  146 . The collet  158  includes an outer surface  160  that engages the inner surface  150  of the baffle  146  and the second inner surface  131  of the body  112 . The collet  158  further includes an oppositely disposed inner surface  162 . Alternatively, the collet  158  may include an internal annular relief (not shown) for capturing the baffle  146  such that the baffle  146  and collet  158  share a common outside diameter. As described previously with respect to the first embodiment, the collet  158  is generally tubular or cylindrical and includes a plurality of circumferentially spaced and longitudinally disposed slots or displacement reliefs  166  formed therein such as by milling or electro-discharge machining. The collet  158  is composed of a material and constructed in a manner to permit inward radial displacement thereof.  
         [0028]    An annular nose piece  176  caps the socket portion  114  of the body  112 . Cap screws  178  thread into the end of the socket portion  114  of the body  112  to hold the nose piece  176  thereto.  
         [0029]    In assembly, the resilient polymeric rings  134  are compressed within the socket portion  114  of the body  112  and positioned into the annular grooves  136 . The diaphragm  138  is then inserted coaxially within the first inner surface  130  of the socket portion  114  in abutment with a first shoulder  182  of the body  112  and in sealing engagement with the polymeric rings  134  to seal the fluid chamber  132 . The baffle  146  is then assembled within the diaphragm  138  and longitudinally centered therealong. The collet  158  is then assembled within the baffle  146 , the first inner surface  130  of the socket portion  114 , and the second inner surface  131  of the socket portion  114  in abutment with a second shoulder  184  of the body  112 . As before, the collet  158  is angularly oriented or clocked with respect to the baffle  146  such that the displacement relief in the baffle  146  is clocked between adjacent displacement reliefs  166  in the collet  158 . Finally, the nose piece  176  is assembled over the end of the socket portion  114  of the body  112 . The cap screws  178  are then threaded through the end of the nose piece  176  and into the end of the socket portion  114  to secure the assembly together. Accordingly, the socket portion  114  of the body  112  carries the various assembled components described above to constitute the chuck  110 .  
         [0030]    In use, the workpiece  100  is disposed within the collet  158  until the workpiece  100  engages the second shoulder  184  of the body  112 . The workpiece  100  may be a cast iron sleeve, or any other workpiece suitable for mounting in a chuck. To firmly hold the workpiece  100  in the chuck  110 , fluid under pressure is provided from an internal or external source through the main fluid passage  122  and branch fluid passages  124 ,  126  and into the fluid chambers  132 . The force of the pressurized fluid radially inwardly displaces the diaphragm  138  which firmly engages and radially inwardly displaces the baffle  146  which, in turn, firmly engages and radially inwardly displaces the collet  158  to urge the collet  158  into firm engagement with an outer surface  104  of the workpiece  100  to firmly hold and accurately locate the workpiece  100  for machining operations to be performed thereon. To remove the workpiece  100  after machining operations, the pressure of the fluid supplied to the chuck  110  is decreased, thereby decreasing the pressure of the fluid in the fluid chamber  132  to thereby relax the diaphragm  138 , baffle  146 , and collet  158 . Thus, the diaphragm  138  acts as a drive member to radially outwardly urge a driven member (collet  158 ) into engagement with the workpiece  100  and the baffle  146  is an intermediate member to prevent the softer diaphragm material from extruding through the reliefs  166  in the collet  158 .  
         [0031]    The baffle or retainer designs of the above described arbor and chuck embodiments add a unique and unobvious feature to the art of arbor and chuck design. Under high performance applications in the absence of the baffle, the fluid pressure forces may be such that the polymeric material of the diaphragm will extrude through the displacement reliefs in the collet thereby permanently damaging the arbor and rendering it unfit for further use. The baffle or retainer provides a simple, inexpensive, and effective way to block the polymeric material from extruding through the displacement reliefs in the collet and thereby bolsters the maximum clamping or gripping force of the arbor and chuck. Accordingly, the arbor or chuck will achieve longer tool life and can handle extremely high fluid pressure conditions to provide greater holding power and a wider range of maximum displacement or contraction, without fluid leaks or extrusion of the diaphragm through the collet.  
         [0032]    While the forms of the invention herein disclosed constitute a presently preferred embodiment, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramification of the invention. It is understood that terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.