Abstract:
A chuck assembly comprising a mandrel portion including an extending member sized and shaped to hold a workpiece; and a piston including a bore receiving the extending member, the piston mounted for supported movement on and relative to the extending member, the piston moving between a first position and a second position, the first position providing for insertion and removal of the workpiece to and from the extending member, the second position causing gripping force to be applied to the workpiece in at least two locations that are spaced longitudinally along the workpiece to inhibit relative movement between the mandrel and the workpiece.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 12/939,158, entitled CHUCK FOR HOLDING PRECISION COMPONENTS filed on Nov. 3, 2010, which claims priority from U.S. Provisional Application No. 61/257,615, filed Nov. 3, 2009, the entire disclosures of which are hereby expressly incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to a chuck for holding components, and specifically to a chuck used to hold components in a machine for precision working of components. 
     BACKGROUND 
     Chucks are mechanisms removably hold and/or secure a part or tool. Some chucks operate by manipulation by the operator to clamp onto and secure and/or unsecure a part or tool. For example, a conventional three jaw chuck requires the operator to loosen the jaws to insert the item to be held and to tighten the jaws to clamp down on and secure the item. Other bit holders may automatically clamp onto and secure an item when the user inserts the item into the chuck, or require an action by the operator, such as twisting the chuck body by hand or using an external device, such as a key or other tool, to secure and/or unsecure an object to be held. 
     SUMMARY 
     According to a first embodiment, a chuck assembly is provided comprising a mandrel portion including an extending member sized and shaped to hold a workpiece; and a piston including a bore receiving the extending member, the piston mounted for supported movement on and relative to the extending member, the piston moving between a first position and a second position, the first position providing for insertion and removal of the workpiece to and from the extending member, the second position causing gripping force to be applied to the workpiece in at least two locations that are spaced longitudinally along the workpiece to inhibit relative movement between the mandrel and the workpiece. 
     According to another embodiment, an assembly for holding a workpiece is provided comprising a mandrel portion including an extending member; a piston including a bore receiving the extending member, the piston mounted for supported reciprocal movement on the extending member, the piston including plurality of tabs having internal and external surfaces, the tabs being able to deflect to bring the internal surfaces into engagement with the extending member; and a set of jaws mounted for pivotal movement, each jaw of the set of jaws including a surface positioned to receive force exerted by the external surfaces of the piston, wherein movement of said piston exerts force via the external surfaces of the piston and causes pivotal movement of said set of jaws. 
     According to yet another embodiment, an assembly for holding a workpiece is provided comprising a mandrel portion including an extending member; a piston including a plurality of tabs cooperating to define a bore receiving the extending member, the piston mounted for supported reciprocal movement on and relative to the extending member; a set of jaws mounted for pivotal movement, wherein movement of said piston causes pivotal movement of said set of jaws, wherein each jaw of the set of jaws includes a clamping surface operable to frictionally engage a workpiece placed within the chuck assembly, pivotal movement of said set of jaws altering an angle assumed by the clamping surface. 
     Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of the chuck assembly according to an exemplary embodiment. 
         FIG. 2  is a perspective view of the chuck assembly. 
         FIG. 3  is a cross-sectional view of the along the longitudinal axis of the chuck assembly. 
         FIG. 4  is an enlarged cross-sectional view of a chuck housing end of the assembly shown in  FIG. 3 . 
         FIG. 5  is a cross-sectional view of a chuck assembly similar to  FIG. 3 . 
         FIG. 6A  is a cross section side view of a mandrel of a chuck assembly according to an exemplary embodiment. 
         FIG. 6B  is a rear view of the mandrel shown in  FIG. 6A . 
         FIG. 6C  is a side view of the mandrel shown in  FIG. 6A . 
         FIG. 6D  is an enlarged view of the circled area of  FIG. 6A . 
         FIGS. 7A to 7D  shows various views of a piston of a chuck assembly according to an exemplary embodiment. 
         FIG. 8A  is a perspective view of a jaw of a chuck assembly according to an exemplary embodiment. 
         FIG. 8B  is a top view of the jaw shown in  FIG. 8A . 
         FIG. 8C  is a cross section view of the jaw shown in  FIG. 8A . 
         FIGS. 8D and 8F  are side views of the jaw shown in  FIG. 8A . 
         FIG. 8E  is a rear view of the jaw shown in  FIG. 8A . 
         FIGS. 9A to 9F  show various views of a housing of a chuck assembly according to an exemplary embodiment. 
         FIGS. 10A and 10B  show a cross section view of a second embodiment chuck assembly employing the piston of  FIGS. 7A-D . 
         FIG. 11A and 11B  another cross section view of the second embodiment chuck assembly of  FIGS. 10A and 10B . 
     
    
    
     DETAILED DESCRIPTION 
     Finish grinding of some injection system components, i.e. injector plungers or needles, requires special work holding and clamping methods to achieve required roundness and end-to-end run out specifications. Some injector needles are quite long, e.g. greater than 130 mm, and small in diameter, e.g. diametral cross section of 4 mm. Needles often include other portions or diametral sections along its length having larger diameters, such as 6 mm and 8 mm. This needle configuration requires a chuck that can receive these extra long parts and have enough chuck jaw travel to accommodate the diametral differences of the different needle sections, and yet be accurate and repeatable to less than 0.005 mm when clamping work pieces. 
     There do not appear to be any standard off-the-shelf clamping devices that perform this work holding function sufficiently to satisfy the above-mentioned requirements. 
     The chuck of the present invention is specifically dedicated to provide proper work holding during needle grinding operations to achieve required roundness and run out specifications. The chuck of the present invention is designed to enable grinding of either end of the needle, also referred to as the needle valve element or plunger. The part to be machined can be simply turned around endwise if necessary. Conventional grinding operations require two distinct operations with different chucks for each end of the needle. The chuck change over between the two grinding operations was minimized and without any additional work holding. 
     Major features of the chuck of the present invention include enabling greater precision machining with accuracy and repeatability (run-outs) of less than 0.005 mm. In addition, the chuck accepts parts (needles) with large length to diameter (L/D) ratios, can hold parts up to 150 mm in length, and has a jaw that opens through a wide range, for example, 6 mm, i.e. a jaw opening of 3 to 9 mm, or 4 to 10 mm, etc. Conventional chucking devices of similar accuracy have an opening range of 0.2 mm. 
     The chuck of the present invention effectively holds small works, such as needle valve elements or plungers used in fuel injectors, thereby improving the extent, accuracy and precision of grinding throughout grinding operations. 
     Referring now to  FIGS. 1-6 , an embodiment of a the chuck includes a mandrel  1 . As shown, the mandrel has a #5 Morse taper to fit a standard work head of the grinding machine, although the taper can alternatively be another size, such as a #4 taper, or a flange mounting may be used. Mandrel  1  also serves as a base mounting for all other chuck components. 
     The chuck also includes a chuck housing  3 , a piston  2  positioned for sliding guided movement on an extension  4  formed on mandrel  1 , and three jaws  5  positioned in, and mounted on, housing  3 . Housing  3  functions as the main chuck body, mounts to the mandrel  1 , and houses jaws  5 . Piston  2  is preferably air actuated but can be actuated by pressurized oil. Piston  2  moves axially along the chuck and mandrel extension  4  between extended and retracted positions to provide motion for, or cause movement of, the chuck jaws  5 . Movement of piston  2  in a forward axial direction toward the extended position away from mandrel  1  causes jaws  5  to close or move toward a closed position. Movement of piston  2  in a reverse axial direction away from mandrel  1  causes jaws  5  to open or move toward an open position. One or more piston return springs  6 , positioned between the housing and a piston flange, biases the piston  2  toward the retracted position away from housing  3  thereby moving the piston  2  in a reverse direction when the air or oil pressure is shut off. 
     Jaws  5  are each pivotally mounted on a jaw retaining assembly  8  (bushings, spacers and/or pins), as shown in  FIG. 1 , to pivot in a radial plane extending radially from the centerline axis of the housing  3 . Each jaw  5  pivots around a pivot axis  11  extending perpendicular to the radial plane so that a clamping end of each jaw  5  moves in a clamping direction toward the centerline axis of the housing  3  when piston  2  moves toward its extended position. 
     Referring now to the  FIGS. 8A to 8F , which show more detailed views of an exemplary jaw  5 , and  FIGS. 9A to 9F , which show detailed views of an exemplary housing  3 , the housing  3  includes three jaw slots  12  formed within the housing and spaced equally around the circumference of the interior of housing  3 . Each jaw slot  12  is sized to receive and guide one of the jaws  5  during pivoting movement. Each jaw retaining assembly  8  (see also,  FIG. 1 ) extends through the housing  3 , a passage  14  formed in the respective jaw, and back into the housing  3  to pivotally mount and retain the jaw within the slot. Thus, jaws  5  can be mounted using precisely fitted bushings  18   a ,  18   b  to ensure stability and repeatability. Each jaw  5  also includes a driven end  13  having a curved inner surface for driven abutment or contact by a tapered portion  16  of a driving end of piston  2  (see,  FIG. 4 ). Preferably the tapered portion is cone, or frusto-conically, shaped, for example, as shown in  FIGS. 7A to 7D . Tapered portion  16  includes a plurality of tabs  30  that are formed via a plurality of gaps  32  formed in tapered portion  16 . Piston  2  also includes a plurality of gaps  34  defined in cylindrical portion  36 . Gaps  32 ,  34  allow tabs  30  to deflect or flex when force is applied that urges tabs  30  radially inward. 
     A jaw return spring  10  is mounted at the driven end in a retaining opening  24  of each jaw to bias the driven end of the jaw toward and into abutment with the driving end of piston  2 , and thus biasing jaw  5  toward a refracted position around pivot axis  11 . 
     A part stop  24  is replaceably positioned within a conical bore formed in the mandrel extension to provide a fixed stop against which the workpiece or part, i.e. injector needle element, is positioned when inserting the part into the chuck. A plurality of interchangeable part stops having different length can be provided. 
     A replaceable jaw insert  9  may be provided on the clamping end of each jaw  5  to accommodate different clamping diameters. Jaw inserts can be attached to the top portion of each jaw  5  using screws  27   a ,  27   b  in openings  28   a ,  28   b  (see,  FIGS. 4 and 8B ) and are designed for quick change over (and replacement) to accommodate different work pieces. A jaw insert adjuster  7 , mounted adjacent each insert  9  at  30  (see,  FIG. 8E ), permits the position of each insert  9  to be adjusted radially to achieve required run outs. This is accomplished by the jaw inserter adjuster  7 . 
     Piston  2  is matched to the mandrel extension or arbor with a minimal clearance to permit smooth sliding yet well supported reciprocal movement. Piston  2  is also designed to collapse onto the mandrel in full closed position to provide stability and repeatability. Controlled air leakage thru the piston/mandrel clearance can be provided to reduce or prevent debris from entering cylinder chamber and ensure free sliding motion. 
     Jaw insert adjuster  7  is a micro adjusting screw to enable zeroing of the radial run out of the work piece to a desired accuracy. A set up detail (spider, not shown) is also designed to fit jaws for jaw grinding under a clamped condition if so desired. The spider is a ring with dowel pins that can be inserted into inner mounting holes of the jaw inserts so the jaws can be closed (clamped) for grinding of jaw inserts. Precisely adjusted jaws  5  will provide radial run out accuracy of 0.005 mm (or better) while maintaining a large range of opening clearance/motion (8 mm diametral) to accommodate different part geometries. 
     In use, the work piece or part  20  is inserted into the chuck against part stop  24 . A part guide  15  may be used as a loading aid to help guide the part  20  into the chuck when manually clamping/loading. Air or pressurized oil is supplied to the piston area through a rotary coupling, air tube/passageway, and internal drillings. For example,  FIGS. 3-6  show an air passageway  17 , which splits into plural passageways before entering the area of the housing  3  near the piston  2 . Upon supplying air pressure, piston  2  moves forward causing the jaws  5  to pivot and clamp the part. Forward movement of piston  2  that engages jaws  5 , further places a radially-inward-directed force on tabs  30 . Such force causes tabs  30  to deflect radially inward to squeeze extension  4  which, in turn grips the workpiece  20  at a proximal end. Accordingly, it will be appreciated that engagement of piston  2  with jaws  5  (which further clamp workpiece  20 ) creates a closed force loop (illustrated at  100 ). The force loop provides that workpiece  20  is gripped at two locations (by the jaws  5  and by tabs  30 ). The force loop further provides that the grip at one grip location cannot be loosened without imparting greater grip force at the second grip location. An illustration of such a force loop is provided in  FIGS. 10A and 10B , which is directed at a second embodiment mandrel  1 ′ that uses the same jaws  5  and piston  20 . 
     For parts that are required to protrude from the chuck, an auxiliary center support  22  can be used. To unclamp the work part, air supply to the chuck is shut off. With the air shut off, piston return springs  6  return piston  2  to its home position, and jaw return springs  10  pivot the jaws back into their home position. 
     A chuck mounted dressing disk may be used for wheel dressing. During chuck set-up, jaw inserts  9  are adjusted for required concentricity using jaw insert adjusting screws  7  and appropriate dial (or digital) indicator. This chuck can be used for precision grinding, turning, or whenever precise clamping of long and slender parts is required. 
     As previously noted,  FIGS. 10A and 10B , shows a second embodiment mandrel  1 ′ that uses the same jaws  5  and piston  2 . Mandrel  1 ′ installs into a grinding machine work head via a Morese Taper. Mandrel  1 ′ includes holes in a flange and is bolted to a face of a machine work head spindle. It should be appreciated that  FIG. 10A  is not a pure cross-section, but rather as shown on  FIG. 10B , is a cross section that changes section at the mid-line of mandrel  1 ′( 10 A- 10 A). This change in section is provided such that multiple jaws  5  are shown. Of course, there are actually three jaws  5  and all jaws  5  participate in the force loop. Again, the force loop provides that workpiece  20  is gripped at two locations (by the jaws  5  and by tabs  30 ). The force loop further provides that the grip at one grip location cannot be loosened without imparting greater grip force at the second grip location. Still further, when engaged, tabs  30  include inner and outer surfaces that are both applying forces that cause gripping of work piece  20 . Inner surfaces of tabs  30  apply force to extension  4  which translates to grip work piece  20 . Outer surfaces of tabs  30  apply force to jaws  5  which are urged to pivot about pivot axis  11  such that jaw insert  9  is urged into and exerts force on workpiece  20 . 
     Mandrel  1 ′ differs from mandrel  1  in the nature of the disengagement of piston  2  and the release of workpiece  20 . As shown in  FIGS. 10A  and B, springs  40  are included that bias piston  2  to an engaged position. Springs  40  are crafted to provide enough force on piston  2  to cause piston  2  to remain in the engaged position absent pneumatic or hydraulic pressure acting thereon. Accordingly, in one embodiment, springs  40  are matched with springs  6  and/or  10  such that regardless of the position of piston  2 , piston  2  is held in such position absent the application of additional force. 
       FIGS. 11A and 11B  show hydraulic/pneumatic pathways  44 ,  46  and pistons  42  that provide additional force to move piston  2  between engaged and disengaged positions. Like  FIGS. 10A and 10B ,  FIG. 11A  is a cross-section that changes section at its midpoint ( 11 A- 11 A). This change in section allows for multiple fluid pathways to be illustrated. Pathway  44  operates similarly to previously discussed passageway  17  such that fluid supplied thereto causes engagement movement of piston  2 . Pathway  46  leads to pistons  42 . In the present embodiment, there are three pistons  42  positioned to selectively engage piston  2 . When pressurized fluid is supplied to pathways  46  and to pistons  42 , pistons  42  extend to urge piston  2  to a disengaged position. 
     While an exemplary embodiment in accordance with the claimed invention has been shown and described, it is understood that the invention is not limited thereto. The present invention may be changed, modified and further applied by those skilled in the art. Therefore, this invention is not limited to the detail shown and described previously, but also includes all such changes and modifications within the scope of the following claims and their equivalents.