Patent Abstract:
An electrode tube holding apparatus is mounted to an electric discharge machine (EDM). The holding apparatus is slidable upward and downward along with the spindle of the EDM and maintained within the midsection of an electrode tube for reducing the deformation of the electrode tube during its movement.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to electric discharge machines (EDM) and more particularly to an electrode tube holding apparatus for an EDM. 
     2. Description of the Related Art 
     A general EDM works like that a rotatable chuck mounted to a spindle thereof holds and drives an electrode tube to rotate and eject high-pressure machining liquid and then electro-discharge machining is applied to a workpiece after the electrode tube is electrified, whereby a deep hole is formed in the workpiece for the machining purpose. Referring to  FIGS. 1-2 , the electrode tube  1  of the conventional EDM is held at the rotatable chuck  2  and at a die guide  4  of a die guide holder  3  below the spindle  5 . As shown in  FIG. 2 , while the electro-discharge machining proceeds, some deviations will occur between the axis of the rotatable chuck  2  and the axis of the electrode tube  1  and such deviations will result in deformation of the electrode tube  1  due to centrifugal effect while the electrode tube  1  is rotated. Although the electrode tube  1  is held by the die guide  4 , the length of the electrode tube  1  causes the centrifugal effect on itself to incur excursion of its distal end, which has become a serious problem. When such excursion is slight, some problems may happen, like deviation of the hole or enlarged diameter of the hole after machining. When such excursion is serious, it may even disable the EDM from normal operation. In this way, the conventional EDM is too unstable to apply the electro-discharge machining to the microminiature hole. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide an electrode tube holding apparatus for an EDM, wherein the electrode tube can avoid deformation. 
     The foregoing objective of the present invention is attained by the electrode tube holding apparatus. The EMD comprises a main body and a rise-and-fall member. The electrode tube holding apparatus comprises a gear wheel, a cantilever, and a rope. The gear wheel is pivotably attached to the rise-and-fall member and has a post. The gear wheel and the post can be rotated along with the movement of the rise-and-fall member. The cantilever is slidably mounted to the main body, having at least one guide hole running therethrough for inserting an electrode tube mounted to the rise-and-fall member. The rope has two ends connected with the cantilever and the post respectively. When the gear wheel is rotated, the post is rotated to wind or unwind the rope to further move the cantilever upward or downward; meanwhile, the cantilever is slidable along the main body and maintained within the midsection of the electrode tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of the conventional EDM. 
         FIG. 2  is a side view of the conventional EDM. 
         FIG. 3  is a front view of a preferred embodiment of the present invention. 
         FIG. 4  is a side view of the preferred embodiment of the present invention. 
         FIG. 5  is a schematic view of the preferred embodiment of the present invention in operation. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIGS. 3-5 , an electrode tube holding apparatus  60  for an EDM in accordance with a preferred embodiment of the present invention comprises a drive assembly  62  and a holding assembly  64 . The EDM comprises a base frame  20 , a spindle  40 , and an electrode tube  80  mounted to the spindle  40 . 
     The base frame  20  includes a main body  22 , a first motor  24 , a screw rod  26 , and a die guide holder  28 . The main body  22  is mounted upright to the EDM and movable along the vertical-axis or the horizontal-axis. The first motor  24  is fixed to a top end of the main body  22 . The screw rod  26  has a top end and a bottom end, the former of which is fixed to an output shaft of the first motor  24  via a coupling and the latter of which is rotatably attached to the main body  22 . The screw rod  26  can be driven by the first motor  24  to rotate clockwise or counterclockwise. The die guide holder  28  is fixed to a bottom side of the main body  22 , having a die guide  282  for inserting the electrode tube  80  therethrough for the electro-discharge machining. 
     The spindle  40  includes a rise-and-fall member  42 , a second motor  44 , and a chuck  46 . The rise-and-fall member  42  is mounted to the screw rod  26  for ascension and descension while the screw rod  26  is rotated. The second motor  44  is mounted to the rise-and-fall member  42 . The chuck  46  can be driven by the second motor  44  for holding the electrode tube  80 . 
     The holding apparatus  60  includes a drive assembly  62  and a holding assembly  64 . The drive assembly  62  has a gear rack  622 , a gear wheel  624 , a post  626  mounted to the gear wheel  624 , and a rope  628 . The gear rack  622  is fixed to a left side of the main body  22 . The gear wheel  624  is pivotably attached to the rise-and-fall member  42  and engaged with the gear rack  622 . The post  626  is rotated along with the gear wheel  624 . The rope  628  is a cable wire in this embodiment, having a top end and a bottom end, the former of which is fixedly connected with the post  626  and the latter of which is mounted to the holding assembly  64 . Along with the rotation of the post  626 , the rope  628  can be wound or unwound to further drive the holding assembly  64 . It is to be noted that the winding/unwinding direction of the rope  628  is converse to the upward/downward moving direction of the rise-and-fall member  42 . Namely, while the rope  628  is wound, the rise-and-fall member  42  is slidably moved downward The diameter of the post  626  is a half of that of the gear wheel  624 , such that the length for which the rope  628  is wound/unwound is a half of the distance for which the rise-and-fall member  42  is moved downward/upward. 
     The holding assembly  64  includes a guide rail  642 , a cantilever  644 , and two holding members  646 . The guide rail  642  is parallel to the gear rack  622  and fixed to a left side of the gear rack  622 . The cantilever  644  has a rear end slidably mounted to the guide rail  642  and fixed to a bottom end of the rope  628  for upward and downward sliding driven by the rope  628 . The cantilever  644  has at least one guide hole running therethrough for inserting the electrode tube  80 . Each of the holding members  646  has one end pivotably attached to a front end of the cantilever  644  for pivoting movement between a holding position and a retaining position on a pivot. While at the holding position, the holding member  646  holds the electrode tube. While at the retaining position, the electrode tube  80  is movable between the two holding members  646  for adjusting the electrode tube to a proper position before it is held. 
     When the EDM machines a workpiece, the workpiece is first fixed to a predetermined position under the spindle  40 ; meanwhile, each of the holding members  646  is at the retaining position, the electrode tube  80  is inserted through the holding member  646  and the die guide  282 , and then the holding member  646  is moved to the holding position. Next, the electrode tube  80  is electrified for discharge machining As shown in  FIG. 5 , when the first motor  24  drives the screw rod  26  to rotate and the rise-and-fall member  42  descends, the bottom end of the electrode tube  80  approaches the workpiece to apply the discharge machining to the workpiece. Meanwhile, the gear wheel  624  pivotally attached to the rise-and-fall member  42  and engaged with the gear rack  622  is driven to rotate the post  626  in such a way that the distance for which the holding member  646  ascends is a half of the distance for which the rise-and-fall member  42  descends. In this way, the holding member  646  remains positioned at a midsection of the electrode tube  80 . 
     In conclusion, the present invention includes the following advantages.
         1. Since the top end, the midsection, and the lower part of the electrode tube  80  are respectively held by the chuck  46 , the holding members  646 , and the die guide  282 , it can indeed reduce the deformation of the electrode tube  80  due to the deviation between the axis of the chuck  46  and the axis of the electrode tube  80 , thus preventing the machined hole from expanding.   2. The holding apparatus of the present invention can lessen the deformation of the electrode tube  80 , such that the electrode tube  80  remains straight to enable the discharge machining to meet the requirement for precision. Under the circumstances, the stability of overall discharge machining can be enhanced.       

     Although the present invention has been described with respect to a specific preferred embodiment thereof, it is in no way limited to the specifics of the illustrated structures but changes and modifications may be made within the scope of the appended claims.

Technology Classification (CPC): 1