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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       APPENDIX 
       [0003]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0004]    1. Field of the Invention 
         [0005]    The present invention pertains to post drivers. More particularly, the present invention pertains to a multipart guide collet that can easily be detached from a post in the event that the end of the post deforms. 
         [0006]    2. General Background 
         [0007]    Post drivers are used to drive posts axially into the earth or other materials. Such posts may be rods, bars, tubes, etc. For example, post drivers are often used to drive rebars into the ground. A typical post driver comprises a hammer that reciprocates and intermittently strikes an anvil. The anvil engages an axial end of the post being driven. The impact loads are thereby transferred from the anvil to the post so as to drive the post. In some cases the anvil is movable relative to the rest of the post driver such that the remainder of the post driver does not experience the impact loads. To eliminate torsion loads on the anvil, the post preferably should be axially aligned with the center of mass of the anvil. Of course, not all posts have the same diameter and it&#39;s therefore desirable to configure a post driver to handle posts of different diameter. Thus, a post driver is often provided with various bolt-on collets/adapters adapted for specific post diameters for radially guiding the post relative to the anvil. On occasion, the end of a post may become mushroomed, which often makes the post difficult to remove from such collets. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention overcomes the disadvantages associated with prior art post drivers by providing a collet that can be removed from a post without axially sliding the post out of the collet. 
         [0009]    In one aspect of the invention, a post driver comprises a main body, an anvil, a hammer, a motor, and a guide collet. The main body has an axial end and a cavity. The axial end has an axial opening configured and adapted to allow a post to be inserted partially in the cavity of the main body therethrough. The anvil is positioned within the cavity of the main body and is configured to be movable axially between first and second positions. The hammer is positioned within the cavity of the main body and is configured to be movable axially in a manner such that the hammer can impact the anvil when the anvil is in its first position. The motor is configured and adapted to axially reciprocate the hammer within the main body in a manner such that the hammer can intermittently impact the anvil when the anvil is in its first position. The guide collet comprises first and second separable parts and is removably attached to the axial end of the main body in a manner such that the guide collet is at least partially positioned within the cavity of the main body and in a manner such that the first and second separable parts are fixed in position relative to each other. The guide collet comprises a collet opening that is aligned with the axial opening of the main body. The collet opening is configured and adapted to allow a post to be inserted partially in the cavity of the main body therethrough in a manner such that the post can contact the anvil when the anvil is in its first position. The first and second parts of the guide collet are separable from each other when the guide collet is detached from the main body in a manner such that the guide collet can be separated from a post passing through the collet opening without axially withdrawing said post from the collet opening. 
         [0010]    In another aspect of the invention, a guide collet for a post driver having a main body configured to partially receive a post therein is attachable to the main body of the post driver and comprises a plurality of parts that collectively form a collet opening when the parts are attached to the main body of the post driver. The collet opening is configured and adapted to slideably receive a post. The parts of the guide collet are separable from each other without tools when the guide collet is detached from the main body of the post driver such that guide collet is capable of being separated from a post that previously extended through the collet opening without sliding an end of the post through the collet opening. 
         [0011]    In yet another aspect of the invention, a method comprises inserting a post partially into a post driver. The post driver comprises a main body having a cavity and guide collet attached to an end of the main body. The guide collet comprises a plurality of parts that collectively form a post opening. The insertion includes passing an end of the post through the post opening of the guide collet and into the cavity in a manner such that post extends through the collet opening. The method further comprises removing the post from the post driver by detaching the guide collet from the main body and separating the parts of the guide such that the removal of the post occurs without passing the end of the post through the opening of the guide collet. 
         [0012]    Further features and advantages of the present invention, as well as the operation of the invention, are described in detail below with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  depicts the preferred embodiment of a post driver in accordance with the invention. 
           [0014]      FIG. 2  depicts a top view of the post driver. 
           [0015]      FIG. 3  depicts a cross-sectional view of the collet assembly and the lower portion of the main body of the post driver taken about the line A-A shown in  FIG. 2 , and shows the anvil in its lowermost position. 
           [0016]      FIG. 4  is a similar cross-sectional view and shows a post passing through the collet assembly and anvil in its uppermost position. 
           [0017]      FIG. 5  is identical to  FIG. 3  except that  FIG. 4  depicts the end of the post being mushroomed. 
           [0018]      FIG. 6  is a perspective view of the post driver with the collet assembly disassembled for the removal of the mushroomed post. 
           [0019]      FIG. 7  is a perspective view of the guide collet members of the post driver. 
       
    
    
       [0020]    Reference numerals in the written specification and in the drawing figures indicate corresponding items. 
       DETAILED DESCRIPTION 
       [0021]    A post driver in accordance with the invention is shown in  FIG. 1 . The post driver  10  comprises a motor  12 , a main body  14 , a handle  16 , and a collet assembly  18 . The motor  12  is represented in box-like form in the figures, but is preferably a gas powered four-stroke internal combustion engine such as a Honda® GX-35 engine. However, it should be appreciated that other motors could be used, including electric, pneumatic, or hydraulic motors. The handle  16  is preferably a single piece of tubing that preferably forms multiple grip portions. More preferably, the grip portions include a pair of horizontal grip portions  20  and a pair of vertical grip portions  22 . The horizontal grip portions  20  are vertically spaced from each other and are preferably also offset horizontally from each other to make it easier to hold and maneuver the post driver  10  while bending over. The vertical grip portions  22  are preferably symmetrically spaced on opposite sides of the main body  14  of the post driver  10 , preferably at or close to the vertical plane defined by the center of gravity of the post driver. 
         [0022]    The main body  14  of the post driver  10  comprises a crankcase  24  and a multipart tube portion  26 . Although not shown in the figures, the crankcase comprises a crank that converts rotational energy into linear reciprocation of a piston. The reciprocation of the piston compresses and decompresses air within the tube portion  26 , which causes a hammer  28  to linearly reciprocate within the tube portion  26 . The main body of the post driver  10  also comprises an anvil  30 . The anvil  30  is preferably movable between two limits of vertical travel (one shown in  FIG. 3  and the other shown in  FIG. 4 ). In at least its uppermost position, the anvil  30  is configured to be impacted by the hammer  28 . The bottom end of the tube portion  26  preferably comprises an attachment portion  32  for securing the collet assembly  18  thereto. The attachment portion  32  is preferably an external threaded portion, but alternatively could be any type of common attachment means such as, for example, a bayonet fitting. A cap  33  is provided on the front of the crankcase  24 . Preferably the cap  33  is configured to be removed from the crankcase  24  by hand and without the use of tools, which allows quick inspection of the oil within the crankcase. Preferably the cap  33  is thread onto the crankcase  24 . 
         [0023]    The collet assembly  18  preferably comprises two guide collet members  34 , which are preferably identical to each other, and a separate attachment member  36 . A shown most clearly in  FIG. 7 , each guide collet member  34  preferably comprises a frustoconical lead-in recess  38  that leads to a semicylindrical channel  40 . Additionally, each guide collet member  34  comprises a rim  42  and a plurality of recesses  44 . When attached to the lower end of the tube portion  26  of the main body  14  of the post driver  10 , the majority of each guide collet member  34  extends into the tube portion of the main body and their semicylindrical channels  40  collectively form a collet opening that, as explained in greater detail below, is adapted and configured to receive a particular post diameter. The rim  42  of each guide collet member  34  is configured to serve as a stop that prevents the collet member from sliding completely into the tube portion  26  of the main body  14  of the post driver  10 . The recesses  44  of the guide collet members  34  merely reduce that material required to form the collet members. Preferably, that material is Delrin® or some other acetal, but other materials would be suitable too. The attachment member  36  is preferably a threaded nut having a graspable exterior that is configured to such that the attachment member can easily be operated by hand. The attachment member  36  threads onto the attachment portion  32  of the main body  14  of the post driver  10  and clamps the rims  42  of the guide collet members  34  to the lower end of the tube portion  26  of the main body  14 , thereby removably securing the collet members  34  to the tube portion. 
         [0024]    In use, a post  46  can be driven by the post driver  10  by inserting an end of the post through the collet opening of the post driver. The posts  46  should have a diameter that is just slightly less than the diameter of the semicylindrical channels  40  of the guide collet members  34 . Of course, various different sized collets are provided to accommodate various post diameters. As a post  46  is being inserted through the collet opening formed by the guide collet members  34 , the frustoconical lead-in portions  38  of the collet members help align the post with the collet opening. As shown in  FIG. 4 , when inserted into tube portion  26  of the post driver  10 , the end of the post  46  will extend through the collet opening and contact the anvil  30  in a manner causing the anvil  30  to move to its uppermost position. The post  46  can then be driven into the ground or other surface by operating the motor  12  of the post driver  10 , which causes the hammer  28  to repetitively strike the anvil  30 , thereby transmitting impact loads from the anvil to the post  46 . Preferably, the collet opening formed by the guide collet members  36  is closely matched to the diameter of the post  46 , but such that the post can freely slide through the collet opening. Closely matching the diameters ensures that the end of the post  46  will be centered relative to the anvil  30 , thereby minimizing any torque acting on the anvil during impact. 
         [0025]    After the post  46  has been driven to its desired depth, the post driver  10  usually can be slid off of the end of the post. However, as depicted in  FIG. 5 , the end of the post  46  may in some cases become mushroomed due to the impacts it has received. If the guide collet was a single piece having a cylindrical opening, the guide collet would then become stuck onto the post  46  since the end of the post would have a larger diameter than the collet opening (assuming the diameter of the collet opening closely matches the diameter of the remainder of the post, which is preferred). With the collet assembly  18  of the present invention, this is not a problem. If mushrooming occurs to such an extent that the end of the post no longer can pass through the opening formed by the semicylindrical channels  40  of the guide collet members  34 , the attachment member  36  can be released from the tube portion  26  of the post driver  10 , and the collet members can then slide completely out of the tube portion. As shown in  FIG. 6 , the guide collet members  34  can then be separated to release the collet members from the post  46  within passing the mushroomed end of the post through the collet opening. Although the mushroomed end of the post still must be passed through the central opening of the attachment member  36  of the collet assembly  18 , this is not a problem since the central opening of the attachment member is much larger than the post diameter. After separating the post from the post driver  10 , the guide collet members  34  can then be reattached to the post driver via the attachment member  36 . 
         [0026]    In view of the foregoing, it should be appreciated that the invention has several advantages over the prior art. 
         [0027]    As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents. 
         [0028]    It should also be understood that when introducing elements of the present invention in the claims or in the above description of exemplary embodiments of the invention, the terms “comprising,” “including,” and “having” are intended to be open-ended and mean that there may be additional elements other than the listed elements. Additionally, the term “portion” should be construed as meaning some or all of the item or element that it qualifies. Moreover, use of identifiers such as first, second, and third should not be construed in a manner imposing any relative position or time sequence between limitations. Still further, the order in which the steps of any method claim that follows are presented should not be construed in a manner limiting the order in which such steps must be performed, unless such an order is inherent.

Summary:
A guide collet for a post driver having a main body configured to partially receive a post therein is attachable to the main body of the post driver and comprises a plurality of parts that collectively form a collet opening when the parts are attached to the main body of the post driver. The collet opening is configured and adapted to slideably receive a post. The parts of the guide collet are separable from each other without tools when the guide collet is detached from the main body of the post driver such that the guide collet is capable of being separated from a post that previously extended through the collet opening without sliding an end of the post through the collet opening.