Abstract:
Some embodiments are directed to a fixing apparatus that includes a threaded adaptor, an arbor having a flange portion and a shaft portion, and a draw cylinder disposed such that rotation of the threaded adaptor moves the draw cylinder in axially upward and downward directions. A collet can be disposed around a periphery of the arbor so as to be coaxial with the draw cylinder, such that movement of the draw cylinder in the axially downward direction causes the draw cylinder to contact the collet and thereby cause the collet to also move in the axially downward direction. The collet can include axially extending channels that define fingers therebetween and interior coaxial surfaces that are configured to communicate with exterior coaxial surfaces of the arbor such that axially downward movement of the collet moves the fingers in a radially outward direction to thereby increase an exterior diameter of the collet.

Description:
BACKGROUND 
       [0001]    The disclosed subject matter relates to apparatus for retaining a workpiece, and methods of use and manufacture thereof. More particularly, the disclosed subject matter relates to methods and apparatus that secure a workpiece in place, such as in the contexts of pallet clamps, robot fingers, CNC tombstone jigs, general work holding and handling devices, etc. 
         [0002]    It may be beneficial or necessary in many different contexts to hold a physical component or element (hereinafter “workpiece”) in place. For example, a workpiece can be held in place on another object, such as on a pallet, to facilitate transportation of the object from one location or orientation to another. The workpiece may need to be held in place, i.e., immobile relative to the pallet, so that the workpiece can be subjected to a separate operation at each of the locations and/or orientations. 
         [0003]    In the context of manufacturing, the workpiece can be repeatedly and precisely indexed and held in place on a pallet for a machining or assembly operation. In some situations, such as where the workpiece is an engine cylinder head, the workpiece may be held in a predefined position and orientation, while being subjected to machining processes and forces (e.g., cutting, drilling, centrifugal forces, vibrational forces, etc.). 
       SUMMARY 
       [0004]    Work-holding devices can be indexed into three different layouts: swinging clamps (such as those configured to be maneuvered on a hydraulically driven pivoting clamp), collet clamps, and mandrel style clamp mechanisms. Each of these work-holding device layouts can be subject to advantage(s) and disadvantage(s) as compared to the other layouts, and can be selected based on performance, maintenance, cost and/or any other appropriate targets set for a particular workpiece. 
         [0005]    Related art work-holding solutions exist in lathe-chucking applications for internal chucking of a workpiece. Some expanding collet assemblies can include an arbor flanged portion for securing the collet assembly to a machine tool spindle. In such a layout, a shaft portion of the arbor, which receives the collet sleeve, is concentric with the machine tool spindle. The spindle may cooperate with some type of centering device, such as a tapered recess on the arbor, to align the spindle with a draw bar that actuates the collet. Axial movement of the draw bar is achieved by hydraulic or pneumatic actuation of the machine tool spindle in the axial direction of the draw bar. 
         [0006]    Different work locating stops, which are sleeve members that are each removably secured to a flange portion of the arbor, are used to engage the collet assembly with different workpieces. The work locating stop is disposed around a collet with space to enable the expanding collet to expand when actuated to grip the workpiece. During a clamping process, the collet can move the workpiece towards the machine tool spindle, in effect pulling the workpiece towards the collet assembly. The work location stop prevents or impedes the workpiece pulling effect because the work location stop provides a repeatable and accurate reference surface against which the workpiece abuts. 
         [0007]    Other work-holding solutions can utilize a serrated mandrel that expands and bites into work hole walls of a workpiece. However, expansion of the serrated mandrel can damage the workpiece, such as by scratching and scarring the workpiece. The control mechanism may also be controlled by a hydraulic or pneumatic drive, which imprecisely drives expansion of the mandrel. 
         [0008]    Related art work-holding devices may be subject to other disadvantages. For example, various components may only be suitable for use in chucking of lathes or other machining tools. In particular, one or more components of a hydraulically-driven collet for chucking tools can be incompatible with: workpiece orientation, a need for securing a workpiece without the use of a locating work stop, work hole configurations utilized in a workpiece pallet in a machining or assembly station, etc. In another example, a swing arm mechanism can interfere with machining processes. 
         [0009]    It may therefore be beneficial to provide a work-holding mechanism that addresses at least one of the above and/or other disadvantages of the related art. For example, it may be beneficial to provide a workpiece holding mechanism that: does not involve swinging clamps (and their resultant interference with manufacturing processes); reduces, impedes or avoids damaging the workpiece; is generally compatible with different operations, etc. 
         [0010]    Some embodiments are therefore directed to a fixing apparatus for removably fixing a workpiece to a pallet using an actuator. The fixing apparatus can include a threaded adaptor that is configured to be rotated by the actuator, and an arbor including a flange portion and a shaft portion that defines exterior conical surfaces. The arbor can define a channel that extends through both the flange and shaft portions. A draw cylinder can be disposed in communication with the threaded adaptor, such that rotation of the threaded adaptor moves the draw cylinder in axially upward and downward directions. The draw cylinder can include a draw shaft that is at least partially disposed within the channel of the shaft portion of the arbor. A collet can be disposed around a periphery of the shaft portion of the arbor so as to be coaxial with the draw shaft. The collet can be disposed such that movement of the draw cylinder in the axially downward direction causes the flanged head of the draw cylinder to contact the collet and thereby cause the collet to also move in the axially downward direction. The collet can include axially extending channels that define fingers therebetween and interior coaxial surfaces that are configured to communicate with the exterior coaxial surfaces of the shaft portion of the arbor, such that axially downward movement of the collet moves the fingers in a radially outward direction to thereby increase an exterior diameter of the collet. 
         [0011]    Some other embodiments are directed to a pallet assembly for removably securing a workpiece. The pallet assembly can include a pallet, an actuator, and a collet assembly that is secured to the pallet. The collet assembly can include a threaded adaptor that is configured to be rotated by the actuator and an arbor including a flange portion and a shaft portion that defines exterior conical surfaces. The arbor can define a channel that extends through both the flange and shaft portions. A draw cylinder can be disposed in communication with the threaded adaptor, such that rotation of the threaded adaptor moves the draw cylinder in axially upward and downward directions. The draw cylinder can include a draw shaft that is at least partially disposed within the channel of the shaft portion of the arbor. A collet can be disposed around a periphery of the shaft portion of the arbor so as to be coaxial with the draw shaft. The collet can be disposed such that movement of the draw cylinder in the axially downward direction causes the flanged head of the draw cylinder to contact the collet and thereby cause the collet to also move in the axially downward direction. The collet can include axially extending channels that define fingers therebetween and interior coaxial surfaces that are configured to communicate with the exterior coaxial surfaces of the shaft portion of the arbor, such that axially downward movement of the collet moves the fingers in a radially outward direction to thereby increase an exterior diameter of the collet. 
         [0012]    Still other embodiments are directed to a method of manufacturing a fixing apparatus that is configured to removably fix a workpiece to a pallet using an actuator. The method can include: configuring a threaded adaptor so as to be rotatable by the actuator; configuring an arbor so as to include a flange portion and a shaft portion that defines exterior conical surfaces, and so that the arbor defines a channel that extends through both the flange and shaft portions; disposing a draw cylinder so as to be in communication with the threaded adaptor, such that rotation of the threaded adaptor moves the draw cylinder in axially upward and downward directions; and configuring the draw cylinder so as to include a draw shaft that is at least partially disposed within the channel of the shaft portion of the arbor. The method can also include: disposing a collet around a periphery of the shaft portion of the arbor so as to be coaxial with the draw shaft, the collet being disposed such that movement of the draw cylinder in the axially downward direction causes the flanged head of the draw cylinder to contact the collet and thereby cause the collet to also move in the axially downward direction; and configuring the collet so as to include axially extending channels that define fingers therebetween and interior coaxial surfaces that are configured to communicate with the exterior coaxial surfaces of the shaft portion of the arbor, such that axially downward movement of the collet moves the fingers in a radially outward direction to thereby increase an exterior diameter of the collet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The disclosed subject matter of the present application will now be described in more detail with reference to exemplary embodiments of the apparatus and method, given by way of example, and with reference to the accompanying drawings, in which: 
           [0014]      FIG. 1  is a perspective view of exemplary collet clamp assemblies installed within a workpiece pallet in accordance with the disclosed subject matter. 
           [0015]      FIG. 2  is a perspective view of a workpiece mounted on the workpiece pallet of  FIG. 1 . 
           [0016]      FIG. 3  is a perspective view of one of the collet clamp assemblies of  FIG. 1 . 
           [0017]      FIG. 4  is a cross-sectional view of the exemplary collet clamp assembly of  FIG. 3 . 
           [0018]      FIG. 5  is an exploded perspective view of the collet clamp assembly of  FIG. 3 . 
           [0019]      FIG. 6  is a detailed cross-sectional view of a draw plug and collet of the collet clamp assembly of  FIG. 3 . 
           [0020]      FIG. 7  is a cross-sectional view of an exemplary collet clamp assembly with the collet in a relaxed state. 
           [0021]      FIG. 8  is a cross-sectional view of an exemplary collet clamp assembly with the collet in an expanded position. 
           [0022]      FIG. 9  is a perspective view of an alternative embodiment of a collet clamp assembly. 
           [0023]      FIG. 10  is a top plan view of the alternative collet clamp assembly of  FIG. 9 . 
           [0024]      FIG. 11  is a bottom plan view of the alternative collet clamp assembly of  FIG. 9 . 
           [0025]      FIG. 12  is a side plan view of the alternative collet clamp assembly of  FIG. 9 . 
           [0026]      FIG. 13  is a cross-sectional view of the alternative collet clamp assembly of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0027]    A few inventive aspects of the disclosed embodiments are explained in detail below with reference to the various figures. Exemplary embodiments are described to illustrate the disclosed subject matter, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a number of equivalent variations of the various features provided in the description that follows. 
       I. Workpiece Pallet 
       [0028]      FIG. 1  is a perspective view of exemplary collet clamp assemblies installed in a workpiece pallet  100  in accordance with the disclosed subject matter; and  FIG. 2  is a perspective view of a workpiece  200  (e.g., article of manufacture, such as an engine cylinder head) mounted on the workpiece pallet  100  in accordance with the disclosed subject matter. The workpiece pallet  100  can include a conveying portion  102  and a workpiece portion  104 . The conveying portion  102  can be connected or secured to a mounting surface  118  of the conveying portion  102  in any appropriate manner, such as but not limited to mechanical fasteners, glue, epoxy, welding, pressure fitting, etc. 
         [0029]    The conveying portion  102  can be formed as a unitary or multi-part body, and be configured in any appropriate shape that can support the workpiece portion  104  and the workpiece  200 , such as at a machining station and/or during transport between different machining stations in a manufacturing transfer system. The conveying portion  102  can include end flange portions  106 , transfer rails  108 , attachment points  110 , and a peripheral extension piece  112 . Each lateral end of the conveying portion  102  includes an end flange portion  106  of identical size, extending a partial or entire width of the conveying portion  102 . A transfer rail  108  can be mounted onto each upper and lower face of each end flange portion  106 . Each transfer rail  108  can extend a partial or entire length of the end flange portion  106 . In order to facilitate precise indexing of the workpiece pallet  100  into machining positions, a peripheral extension piece can be located on a side of conveying pallet  102 . Additionally, attachment points  110  can be formed in the transfer rails  108  for receiving locating pins or other locating apparatus at a machining station and/or to aid with motion during transfer between machining stations. 
         [0030]    The workpiece portion  104  can be formed as a unitary or multi-part body, and be configured in any appropriate shape that can support the workpiece  200 , such as at a machining station and/or during transport between different machining stations in a manufacturing transfer system. The workpiece portion  104  can include mounting fixtures  114 , grooves  122 , and one or more collet clamp assemblies  116 . The one or more grooves  122  can be provided in workpiece portion  104  for indexing the workpiece pallet  100  into machining positions or to accommodate transport between different machining stations. A mounting surface  120  can be provided with one or more mounting fixtures  114  that are arranged in any manner for supporting mounting points on the workpiece  200 . The workpiece portion mounting surface  120  can also include one or more collet clamp assemblies  116  arranged in any appropriate locations that correspond to work holes in workpiece  200 . For example, the collet clamp assembly  116  locations can conform to a pattern that can distribute the weight of the workpiece  200  across the workpiece pallet  100 . As described in more detail below, each collet clamp assembly  116  can attach to the workpiece pallet  100  in any appropriate manner, such as but not limited to mechanical fasteners, glue, epoxy, welding, pressure fitting, etc. 
         [0031]    The workpiece  200  can be any article that can be secured in a machining position and moved between assembly and/or machining stations as part of a manufacturing transfer system. In an embodiment, the workpiece  200  can include an engine block or portions thereof that can be mounted onto workpiece pallet  100 . Other workpieces  200  can include any article of manufacture that can be secured onto the workpiece portion  104  by collet clamp assembly  116 . 
       II. Collet Clamp Assembly 
       [0032]      FIG. 3  is a perspective view of one of the collet clamp assemblies of  FIG. 1 , and  FIG. 4  is a cross-sectional view of the collet clamp assembly of  FIG. 3 . An embodiment of the collet clamp assembly  116  can include an arbor  300 , a draw bar  404 , a draw plug  402 , a collet  310 , a stopper bushing  312 , a socket  406 , and a threaded adapter (e.g., a double lock nut)  324 . As will be explained in detail below, during operation the collet clamp assembly  116  can be fixed to a rotating drive mechanism, such as a servo screw drive, that can be removably attached to the draw bar  404  via a double lock nut  324  or other attachment mechanism, in any manner, such as but not limited to mechanical fasteners, glue, epoxy, welding, pressure fitting, etc. 
         [0033]    The arbor, or housing,  300  can include a flange portion  302 , a cylindrical portion  306 , and a shaft portion  304 . The shaft portion  304  extends on one side of the flange portion  302  and the cylindrical portion  306  extends from an opposite side of the flange portion  302 . The shaft portion  304  is concentric with the axis of rotation of double lock nut  324  and/or an external screw drive mechanism. A plurality of mounting holes  308  disposed in the flange portion  302  can be aligned with a plurality of threaded holes in workpiece portion  104  that cooperate with a plurality of bolts for securing the arbor  300  to the workpiece pallet  100 , as best shown in  FIG. 1 . 
         [0034]    The draw bar  404  is disposed in a recess, such as central bore  400 , and is secured at its head to the draw plug  402 , which is disposed in shaft portion  304  in any appropriate manner, such as but not limited to mechanical fasteners, glue, epoxy, welding, pressure fitting, etc. The draw bar  404  is disposed within a recess in the arbor (e.g., central bore  400 ). 
         [0035]      FIG. 5  is an exploded perspective view of the collet clamp assembly of  FIG. 3 , and shows the draw bar  404  that includes a cylindrical shaft portion  512 , a keyed (e.g., alternating key and slot) portion  508  disposed at an end of the draw bar  404  disposed towards the shaft portion  304 , and an enlarged diameter shaft portion  510  disposed between the cylindrical shaft portion and the keyed portion  508 . 
         [0036]    The arbor stepped bore portion  416  includes a keyed receiver  430  that includes keys and slots disposed circumferentially that mirror keys and slots on the draw bar keyed portion  508 . The arbor keyed receiver  430  can slidably receive the draw bar keyed portion  508  in a tongue-in-groove coupling. When coupled, the keyed receiver  430  impedes prevents rotational or lateral motion when the draw bar  404  is actuated. 
         [0037]    The draw bar enlarged shaft portion  510  is received by socket  406 , which is disposed within an expanded central bore  432  of arbor  300 . The socket  406  includes a flanged head  408 , reduced base  410 , and hole  516  that is central to a longitudinal axis, and a notch  514 , as best shown in  FIG. 5 . The socket  406  can support the draw bar  404  within the expanded central bore  432  and maintain the draw bar&#39;s axial alignment to the longitudinal axis of the arbor shaft portion  304  and an external servo screw drive. The socket hole  516  is sized to receive the draw bar  404 , as described above, and to permit axial sliding motion therein when the draw bar  404  is actuated. 
         [0038]    An adapter  322  functions to secure tapered adapter  414  against socket flanged head  408  within the expanded central bore  432 . The notch  514  can receive a pin that can contact and oppose axial rotation of the socket  406 . At least one pair of tapered roller bearings  412  is disposed between tapered wall  424  of the expanded central bore  432  and tapered adapter  414 . Retainer clips  426  may be disposed between socket adapter  322  and tapered adapter  414  to secure the adapters in place. The socket adapter  322  may be attached to socket  406  in any appropriate manner, such as but not limited to threaded fittings, mechanical fasteners, glue, epoxy, welding, pressure fitting, etc., or no fasteners. The socket adapter  322  can also function as a seal to impede or prevent any debris, such as metal chips, fluids, etc., from entering the arbor  300  during the assembly and/or machining processes. 
         [0039]    The base of the draw bar  404  can be threadably attached to the double lock nut  324  using cooperating screw threads. Double lock nut  324  can include a first part  420  that is disposed towards arbor  300  and a second part  422  that is disposed on a base of draw bar  404 . The double lock nut first part  420  can maintain its position when the double lock nut second part  422  is rotated in a first direction (e.g. clockwise) or in a second direction (e.g., counterclockwise). When rotational motion of double lock nut second part  422  is initiated, longitudinal motion of draw bar  404  is actuated using the force of the threaded connection between the draw bar  404  and the double lock nut second part  422 . 
         [0040]    The arbor shaft portion  304  extends in a generally perpendicular direction away from flange portion  302  and includes a central bore  428  that is axially aligned with draw bar  404 . The draw plug  402  is disposed axially through the arbor  300  in an opening in the shaft portion  304  and includes a flanged head  316  that is disposed at an exposed end, a draw plug shaft  500 , and an opposite end that can include a reduced shaft portion  502 . The reduced shaft portion  502  can be received by a recess in the draw bar keyed portion  508  and secured in any appropriate manner. such as but not limited to mechanical fasteners, glue, epoxy, welding, pressure fitting, etc. In an embodiment, the flanged head  316  may include a slot  314  for receiving a tool to turn the draw plug  402  within the draw bar  404 . The collet  310  can be axially slidably disposed around the shaft portion  304 . The flanged head  316  can engage an end of collet  310  as the draw bar  404  actuates the draw plug  402 . 
         [0041]    In an embodiment, the collet  310  is concentric with a servo screw drive when the collet  310  is installed on the shaft portion  304 , based on the fact that the shaft portion  304  should be concentric with the servo screw drive axis. Adjustments for concentricity are therefore advantageously avoided during installation and operation. 
         [0042]    An anti-rotation pin  320 , disposed radially adjacent to a collet first frusto-conical surface  604  (See  FIG. 6 ), provides a stop for the collet  310 , i.e., to advantageously provide a limit to rotational motion of the collet  310  as it is actuated axially by the draw plug  402  on the shaft portion  304 . The anti-rotation pin  320  is advantageously sealed in its pin slot  318  disposed in the collet  310  to impede or prevent debris from entering the inside of the arbor  300 . The anti-rotation pin  320  protrudes above the surface of the shaft portion  304  and is disposed through pin slot  318  into a pin hole  418  in the draw plug  402 . 
         [0043]    The collet  310  includes a plurality of alternating slots  506  that form a plurality of adjacent gripping fingers  504  extending inwardly from opposite collet ends and are alternately interconnected at their top edge portions or bases, as best shown in  FIG. 5 . While the collet  310  is disclosed with eight gripping fingers  504  in  FIG. 5  for sake of clarity, the collet  310  can include a greater or fewer number of gripping fingers  504 , which can be tailored to facilitate relative ease of operation in a work space for a certain workpiece. For example, a greater number of gripping fingers  504  can provide a relatively greater gripping range within a work space of a workpiece  200 . 
         [0044]      FIG. 6  is a detailed cross-sectional view of a draw plug and collet of the collet clamp assembly of  FIG. 3 . The arbor shaft portion  304  includes a pair of annular and parallel frusto-conical surfaces disposed radially inwardly in the direction away from the flange portion, a first frusto-conical surface  600  disposed at its free end and a second frusto-conical surface  602  disposed adjacent to the flange portion  302 , that cooperate with corresponding first frusto-conical surface  604  and second frusto-conical surface  606  on the collet  310 , as best shown in  FIG. 6 . The collet  310  expands when it rides upon the frusto-conical surfaces  600  and  602  as it is actuated by the draw plug  402 . The collet  310  may be constructed out of a material that provides a limited degree of resilience, thereby allowing the collet to return to an original shape when shifted from a first position to a second position, for example from an expanded position to a relaxed state, and any position between the expanded position and the relaxed state. 
         [0045]    The stopper bushing  312  is a sleeve member secured to the arbor shaft portion  304  adjacent to the flange portion  302  in any appropriate manner, such as but not limited to mechanical fasteners, glue, epoxy, welding, pressure fitting, etc. The stopper bushing  312  can function to impede or prevent the base of collet  310  from moving longitudinally, which could displace the collet  310  from its intended location. The stopper bushing  312  also provides a stop for the collet  310  when draw bar  404  is actuated, which causes the collet  310  to expand laterally and grip a workpiece. The stopper bushing  312  may be advantageously removably secured to the arbor  300  such that different stopper bushings and collets may be used depending on the needs of different workpieces. Thus, to machine a different workpiece, the entire collet clamp assembly  116  need not be disassembled nor separated from a servo drive mechanism; only the stopper bushing  312  and/or collet  310  need be replaced. Furthermore, replacement of the stopper bushing  312  and/or collet  310  due to wear and tear can be readily accomplished. 
         [0046]    Because the draw bar  404  is mechanically actuated in an axial direction by a servo screw drive, precise control over longitudinal motion of the draw bar  404 , and in turn draw plug  402 , can be accomplished. In the embodiments, the draw plug flanged head  316  can travel a maximum stroke distance  608 , as best shown in  FIG. 6 . This precise control is accomplished via threaded cooperation between draw bar  404  and double lock nut  324 . 
       III. Alternative Embodiment for a Collet Clamp Assembly 
       [0047]    An alternative embodiment, which introduces some minor variations to the above-disclosed subject matter, is disclosed in  FIGS. 9-13 . Similar parts or elements in these figures retain the same identification as provided in the previously disclosed figures.  FIG. 9  is a perspective view of the alternative embodiment of a collet clamp assembly,  FIG. 10  is a top plan view of the alternative collet clamp assembly of  FIG. 9 , and  FIG. 11  is a bottom plan view of the alternative collet clamp assembly of  FIG. 9 . 
         [0048]    An alternative embodiment of the collet clamp assembly  900  can include an arbor  906 , a single-piece draw bar  1002 , the collet  310 , a single piece socket  1302  (see  FIG. 13 ), and the threaded adapter (e.g., the double lock nut)  324 . As will be explained in detail below, during operation, the collet clamp assembly  900  is fixed to a rotating drive mechanism, such as a servo screw drive, that can be removably attached to the threaded adapter  324  in any manner, such as but not limited to threaded connections and mechanical fasteners. 
         [0049]    The arbor, or housing,  906  can include a flanged portion  902 , a cylindrical portion  904 , and a shaft portion  1304  (see  FIG. 13 ). The shaft portion  1304  extends on one side of the flanged portion  902 , and the cylindrical portion  904  extends from an opposite side of the flanged portion  902 . The shaft portion  1304  is concentric with the axis of rotation of the double lock nut  324  and/or an external screw drive mechanism. A plurality of attachment screws  920  (or bolts, etc.) disposed in the flange portion  902  can be aligned with a plurality of threaded holes in workpiece portion  104  that cooperate for securing the arbor  906  to the workpiece pallet  100 , as best shown in  FIG. 1 . A plurality of housing screws  918  (or bolts, etc.) disposed in the flange portion  902  can be aligned with a plurality of threaded holes in cylindrical portion  904  that cooperate for securing the flange portion  902  to the cylindrical portion  904 . 
         [0050]      FIG. 10  illustrates a top plan view of the single piece draw bar  1002 , flanged head  912 , and lock nut  914 .  FIG. 11  illustrates a bottom plan view of the collet clamp assembly  900  that includes the double lock nut  324 , a single draw bar base portion  1346 , a servo drive connector sleeve  1100  and servo drive protector  1102 . The servo drive connector sleeve  1100  can receive a complementary connector from a servo drive mechanism and servo drive protector  1102  can function to enclose the double lock nut  324  to prevent dirt and debris from entering arbor  906 . 
         [0051]      FIG. 12  is a side plan view of the alternative collet claim assembly  900  of  FIG. 9 ; and  FIG. 13  is a cross-sectional view of the alternative collet claim assembly  900  of  FIG. 9  that includes the single piece draw bar  1002  disposed axially within a recess of the arbor (e.g., in a central bore  1342  and shaft portion central bore  1324 ), and an adapter housing  1200 . The single piece draw bar  1002  includes a head portion  1344 , the base portion  1346 , the keyed portion  1004 , and an enlarged shaft portion  1330  disposed between the head  1344  and the base  1346 . The head portion  1344  is slidably received by the arbor shaft portion  1304  and capped with a flanged head  912  and lock nut  914  or any appropriate manner to secure flanged head  912  to the single piece draw bar  1002 , such as by mechanical fasteners, glue, epoxy, welding, pressure fitting, etc. The flanged head  912  can function similarly to the draw plug flanged head  316  of the previously disclosed exemplary embodiment. 
         [0052]    As disclosed above, the arbor shaft portion  1304  includes a central bore  1324  or recess that can slidably receive the head portion  1344  of the single piece draw bar  1002 . The expanding collet  310  can be axially slidably disposed around the shaft portion  1304 . The flanged head  912  can engage an end of collet  310  disposed away from the flanged portion  902  to pull the collet against a stop, such as stopper bushing  312 . 
         [0053]    The collet  310  includes a plurality of alternating slots  506  that form adjacent gripping fingers  504  extending inwardly from opposite collet ends and are alternately interconnected at their top edge portions or bases, as best shown in  FIG. 5 . In the alternative embodiment, the collet  310  is concentric with a servo screw drive when the collet  310  is installed on the shaft portion  1304 , based on the fact that the shaft portion  1304  is concentric with the arbor&#39;s  906  longitudinal axis. Adjustments for concentricity are therefore advantageously avoided during installation and operation. 
         [0054]    The shaft portion  1304  includes a pair of annular and parallel frusto-conical surfaces disposed radially inwardly in the direction away from the flange portion, including a first frusto-conical surface  1334  disposed at its free end, and a second frusto-conical surface  1336  disposed adjacent the flange portion  902 , which cooperate with corresponding first frusto-conical surface  604  and second frusto-conical surface  606  on the collet  310 . 
         [0055]    An anti-rotation pin  1300  is advantageously disposed in the collet  310  and sealed to impede or prevent debris from entering the inside of the arbor  300 . The anti-rotation pin  1300  protrudes above the surface of the shaft portion  1304  and can be disposed in the single piece draw bar  1002 . 
         [0056]    The collet  310  expands when it rides upon the first and second frusto-conical surfaces  1334  and  1336  as it is actuated by the single piece draw bar  1002 . Although the collet  310  is disclosed with eight gripping fingers  504  in  FIG. 5  for sake of clarity, the collet  310  can include a greater or fewer number of gripping fingers  504 , which can be tailored for relative ease of operation in a work space of a certain workpiece. For example, a greater number of gripping fingers  504  can provide a relatively greater gripping range within a work hole  700  of a workpiece  200 . Furthermore, the collet  310  may be constructed out of a material that provides a limited degree of resilience, thereby allowing the collet to return to an original shape when shifted from a first position to a second position, for example from an expanded position to a relaxed position. 
         [0057]      FIG. 10  further illustrates the longitudinally keyed (e.g., alternating key and slot) portion  1004  disposed on single piece draw bar  1002 , and  FIG. 13  shows the single piece draw bar  1002  and arbor  906  in cross-section. The arbor recess or expanded central bore  1342  includes a keyed receiver  1326  that includes keys and slots disposed circumferentially that can mirror the keys and slots disposed on the draw bar keyed portion  1004 . The arbor keyed receiver  1326  can axially slidably receive the single piece draw bar keyed portion  1004  in a tongue-in-groove coupling. When coupled, the keyed receiver  1326  impedes or prevents rotational or lateral motion when the single piece draw bar  1002  is actuated. Alternatively or concurrently, a key hole  1000  can receive a pin (or bolt, etc.) that can contact and oppose axial rotation of the single piece draw bar  1002 . 
         [0058]    In the bore  1342 , a stop adapter  1332  is disposed between the keyed portion  1004  and enlarged shaft portion  1330 . The single piece draw bar  1002  can move axially in one direction until the enlarged shaft portion  1330  encounters the stop adapter  1332 , and can move in an opposite direction until the keyed portion  1004  encounters the stop adapter  1332 . 
         [0059]    The enlarged shaft portion  1330  can be disposed within single piece socket  1302 , which is disposed within the expanded central bore  1342 . The single piece socket  1302  includes a flanged head  1348 , reduced base  1350 , and hole  1352  that is central to a longitudinal axis, as best shown in  FIG. 13 . The single piece socket  1302  can support the single piece draw bar  1002  within expanded central bore  1342  and maintain the single piece draw bar&#39;s axial alignment to the arbor shaft portion  1304  and an external servo screw drive. The socket hole  1352  is sized to receive the single piece draw bar  1002  and to permit axial sliding motion therein when the single piece draw bar  1002  is actuated. The single piece socket  1302  can be secured within expanded central bore  1342  with a series of spacers and/or adapters. 
         [0060]    An adapter  1312  functions to secure the head portion  1348  of the single piece socket  1302  in axial alignment with the shaft portion  1304 . Adapters  1314  and  1316  are disposed at distal ends of a spacer  1320  to secure the reduced base  1350  of the single piece socket  1302  in axial alignment with the shaft portion  1304 . Spacer  1320  can include a bushing  1318  to secure spacer  1320  between single piece socket  1302 . 
         [0061]    One or more adapters  1316  can function as a seal to impede or prevent debris, such as metal chips, fluids, etc., from entering the arbor  906  during assembly and/or machining operations. Additionally, O-ring  1308  disposed around single piece draw bar head  1344 , and O-ring  1310  disposed around keyed receiver  1326 , can function as seals to impede or prevent debris, such as metal chips, fluids, etc., from entering arbor  906  during assembly and/or machining operations. 
       IV. Operation 
       [0062]      FIGS. 7 and 8  illustrate the operation of the exemplary embodiment for a collet clamp assembly  116 , and in particular  FIG. 7  is a cross-sectional view of an exemplary collet clamp assembly  116  in a first position with collet  310  in a relaxed state, and  FIG. 8  is a cross-sectional view of an exemplary collet clamp assembly  116  in a second position, actuated into an expanded, or gripping, position. The operation is initially disclosed below in the context of the embodiment shown in  FIGS. 1-6 . 
         [0063]    The threaded adapter (e.g., double lock nut)  324  can be secured to a servo screw drive or other precisely-controlled rotating mechanism. In particular, the first part  420  of double lock nut  324  can be secured to draw bar  404 , and the second part  422  can be secured to a servo drive mechanism. To place the collet  310  into a relaxed state, the draw bar  404  is actuated by rotating a servo screw drive in a first rotatable direction (e.g., a counter clockwise direction). To move draw bar  404 , a servo screw drive rotates the double lock nut second part  422  in the first rotatable direction to actuate motion of the draw bar  404  via the threaded connection between draw bar  404  and double lock nut  324 . The draw bar  404  moves along an axial direction aligned with shaft portion  304 , thereby moving the draw plug flanged head  316  away from an end of the collet  310 . When the flanged head  408  no longer contacts the collet  310 , tension is removed from the collet  310 , and the collet  310  rides off of the first and second frusto-conical surfaces  600  and  602 , placing the collet  310  into a relaxed state. 
         [0064]    The workpiece  200  may be mounted to each collet clamp assembly  116  after each collet  310  on workpiece  200  is placed into a relaxed state. To mount the workpiece  200  to the workpiece pallet  100 , the workpiece  200  can be positioned vertically over the workpiece portion  104 , such that a pattern of one or more work holes  700  in workpiece  200  align with a corresponding pattern of one or more collets  310  of one or more collet clamp assemblies  116  disposed in workpiece pallet  100 . The workpiece  200  is then lowered so that each work hole  700  can be mounted on an intended collet  310 , as best shown in  FIG. 7 . The collet  310  should travel fully into the work hole  700 , so that the highest frictional holding force can be exerted by the collet  310  on the workpiece  200 . 
         [0065]    To place the collet  310  into a gripping position, the double lock nut second part  422  is rotated by a servo screw drive in a second rotatable direction (e.g., a clockwise direction), and the draw bar  404  pulls the draw plug  402  towards the flanged portion  302 . The draw plug flanged head  316  pushes the collet towards stopper bushing  312 . The force of the flanged head  316  causes the collet  310  to expand when it rides upon the first and second conical surfaces  600  and  602 . In an expanded or gripping position, the collet gripping fingers  504  grip the workpiece  200  using friction forces on inner walls of work hole  700 . Because the workpiece  200  initially abutted the mounting fixtures  114 , the workpiece  200  will remain in the same place during the collet clamping operation, ensuring that each workpiece  200  is located accurately every time, which is best shown in  FIG. 8 . The parallel first and second conical surfaces  600  and  602 , cooperating with the first and second collet conical surfaces  604  and  606 , advantageously provide parallel gripping of the workpiece  200  in the grip range, ensuring accurate gripping with uniform pressures. 
         [0066]    To release the workpiece  200  from the collet  310 , the collet  310  is again placed into a relaxed state. A servo screw drive may be rotated in the first rotatable direction (e.g., counterclockwise), which actuates the draw bar  404 . As a result, the draw bar  404  moves axially towards the flanged portion  302 , thereby moving the draw plug  402  away from an end of the collet  310 . As the draw plug flanged head  316  ceases contact with the collet  310 , the collet  310  rides down the first and second conical surfaces  600  and  602  and returns to its normal, relaxed shape, causing the collet gripping fingers  504  to release their grip on the inside walls of work hole  700 . The anti-rotation pin  320  advantageously impedes or prevents relative rotation between the collet and the shaft portion  304  during the de-clamping operation. At this point, the workpiece  200  can be easily removed from the workpiece pallet  100 . 
         [0067]    The alternative embodiment for the collet clamp assembly  900  (shown in  FIGS. 9-13 ) operates in a manner that is similar to the operation disclosed above. The threaded adapter (e.g., the double lock nut)  324  of the collet clamp assembly  900  can be secured to a servo screw drive or other precisely-controlled drive mechanism. To place the collet  310  into a relaxed state, the single piece draw bar  1002  is actuated by rotating a servo screw drive in a first rotatable direction (e.g., a counter clockwise direction). A first part  420  of double lock nut  324  can be secured to the single piece draw bar  1002 , and a second part  422  can be secured to a servo drive mechanism. To move the single piece draw bar  1002 , a servo screw drive rotates the double lock nut second part  422  in the first rotatable direction to actuate motion of the single piece draw bar  1002  via the threaded connection between the single piece draw bar  1002  and second part  422 . As a result, the single piece draw bar  1002  moves axially away from the double lock nut  324 , thereby moving the flanged head  912  away from an end of the collet  310 . When the flanged head  912  no longer contacts the collet  310 , tension is removed from the collet  310 , and the collet rides off of the first and second frusto-conical surfaces  600  and  602 , placing the collet  310  into a relaxed state. 
         [0068]    To place the collet  310  in an expanded position, double lock nut second part  422  is rotated by a servo screw drive in a second rotatable direction (e.g., a clockwise direction), axially moving the single piece draw bar  1002  towards the double lock nut  324 . The flanged head  912  engages and pushes the collet  310  towards stopper bushing  312 , causing the collet  310  to expand when it rides upon the conical surfaces  1334  and  1336 . The collet gripping fingers  504  then grip the workpiece  200  using friction forces on inner walls of a work hole (e.g., work hole  700 ). The parallel first and second conical surfaces  1334  and  1336 , cooperating with the first and second collet conical surfaces  604  and  606 , advantageously provide parallel gripping of the workpiece  200  in the grip range, ensuring accurate gripping with uniform pressures. 
         [0069]    To release the workpiece  200  from the collet  310 , a servo screw drive is rotated in the first rotatable direction (e.g., counterclockwise), which actuates the single piece draw bar  1002  to move in the first axial direction. As a result, the single piece draw bar  1002  moves axially from double lock nut  324 , thereby moving the flanged head  912  away from an end of the collet  310 . As the flanged head  912  moves away from the collet  310 , the collet  310  rides down the conical surfaces  1334  and  1336  and returns to its normal, relaxed shape causing the collet fingers  504  to release their grip on the inside walls of the work hole  700 . The anti-rotation pin  320  advantageously impedes or prevents relative rotation between the collet and the shaft portion  1304  during the de-clamping operation. At this point, the workpiece  200  can be easily removed from the workpiece pallet  100 . 
         [0070]    The disclosed embodiments can advantageously provide an alternative method of work-holding. Uses for the disclosed embodiments can include, but are not limited to, workpiece pallet clamps, robot fingers, CNC tombstone jigs, and general work-holding/handling devices. The collet claim assembly of the embodiments utilizes a screw mechanism that is capable of providing various advantages, including but not limited to achieving very high torque loads, which can translate as higher gripping forces, without (or with reduced) biting or scarring of the workpiece. 
       V. Alternative Embodiments 
       [0071]    While certain embodiments of the invention are described above, and  FIGS. 1-13  disclose the best mode for practicing the various inventive aspects, it should be understood that the invention can be embodied and configured in many different ways without departing from the spirit and scope of the invention. 
         [0072]    For example, embodiments are disclosed above in the context of a collet with an exterior cylindrical shape. However, embodiments are intended to include or otherwise cover any shape of collet, such as but not limited to square, hexagonal, special shapes, etc., to suit the workpiece being gripped. Further, embodiments are disclosed above in the context of a collet constructed of spring steel. However, embodiments are intended to include or otherwise cover any type of flexible binding medium for a collet, such as but not limited to synthetic or natural rubber. 
         [0073]    Embodiments are disclosed above in the context of an expanding collet. However, exemplary embodiments also are intended to include or otherwise cover other types of collets, such as tapered steel blocks held in a circular position by a flexible binding material, or an internal collet formed as a truncated cone that can be inserted into a work hole with an inner tube and an outer tube. The inner tube can expand with the force of the collet, pushing against the outer tube, which is held by friction forces of the expanded inner tube. 
         [0074]    In the exemplary embodiment of  FIGS. 1-6 , the collet clamp assemblies  116  are arranged in a substantially vertical alignment in workpiece pallet  100 . However, embodiments are intended to include or otherwise cover any appropriate positioning of the collet clamp assemblies  116  relative to the workpiece pallet  100 . 
         [0075]      FIG. 1  shows four collet clamp assemblies  116  disposed in each quadrant of workpiece pallet  100 . Alternative embodiments may include a fewer or greater number of collet clamp assemblies  116  arranged in similar or different patterns that are appropriate for a certain workpiece  200 . For example, more than four collet clamp assemblies  116  can be provided on workpiece pallet  100 , or fewer collet clamp assemblies  116  can be provided. 
         [0076]    In the exemplary embodiment of  FIG. 4 , the draw bar  404  is slidably secured by socket  406 , and in  FIG. 13  the single piece draw bar  1002  is slidably secured by single piece socket  1302 . However, embodiments are intended to include or otherwise cover one or more adapters, sleeves, and/or reducing bushings that can slidably secure a draw bar aligned with a longitudinal axis of an arbor. 
         [0077]    Exemplary embodiments are intended to include or otherwise cover any type of rotating drive mechanism and control system therefore that can couple to the draw bar  404  or single piece draw bar  1002 . Exemplary embodiments are also intended to include or otherwise cover any type of coupling mechanism that couples a rotating drive to the draw bar  404  or single piece draw bar  1002 . 
         [0078]    Exemplary embodiments are further intended to cover omission of any one or both of the engine cover and the middle cover. 
         [0079]    While the subject matter has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. All related art references discussed in the above Background section are hereby incorporated by reference in their entirety.