Abstract:
A method and apparatus for automatically re-pointing twist drill bits includes a drill support mechanism including means for rotatably and axially translatably holding the shank of a drill bit, and a fluted portion receiver for supporting the fluted front cutting portion of the drill bit. The apparatus also includes an optical sensor unit which views the tip and blade part of the drill bit with the drill support mechanism in an off-line position, i.e., rotated away from a grinding wheel station. Responsive to error correction servo command signals received from a comparison of the actual orientation of drill bit cutting lips with a desired pre-determined template position, rotary and linear actuators in the drill support mechanism rotate the drill bit to the proper angular orientation, and advance the bit axially to a pre-determined protrusion length. Also, command signals to the fluted portion receiver elevate the drill bit point to a pre-determined elevation, whereupon a linear actuator cylinder linked via a pivot pin to the drill support mechanism rotates the latter to thereby place the properly oriented drill bit in contact with grinding wheels of a sharpening unit. After each of the grinding wheels has sequentially contacted the cutting edges and point of the drill bit and resurfaces the contacted areas to a desired sharpness, the linear actuator cylinder is used to rotate the drill support mechanism to the off-line position, whereupon a shank retainer is pivoted vertically away from the drill bit shank, allowing the re-conditioned bit to be removed and replaced with another bit to be re-pointed.

Description:
BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The present invention relates to devices and methods for sharpening or re-pointing twist drill bits. More particularly, the invention relates to an apparatus for automatically re-pointing twist drill bits. 
     B. Description of Background Art 
     Printed wiring boards (PWB&#39;s) used to hold and electrically interconnect electronic circuit components are typically fabricated as laminated stacks of copper foil sheets alternating with insulating sheets made of fiberglass, the latter containing glass fibers solidified with a resin such as epoxy. The glass fibers are highly abrasive, and can quickly dull drill bits used to drill holes in the PWB for receiving component leads, or for forming passageways or vias through the PWB. A typical PWB has a thickness of about 0.062 inch, and has hundreds of holes drilled through it. Each contact with the upper surface of a PWlB to drill a hole is referred to as a “hit.” Since PWB&#39;s are usually arranged in stacks of two to five boards for drilling, a corresponding number of holes are drilled for each hit. Because the abrasive nature of the PWB board materials dulls typical drill bits after about 3000-5000 holes are drilled, the drill bit must be removed from service and re-sharpened after about 1,500-2,000 hits. 
     In conventional drill bit grinding apparatuses used to sharpen or re-point twist drill bits, the drill bit must be held in a chuck. Consequently, the operator must manually perform operations such as inserting the drill into the chuck of a drill bit holder mechanism, tightening the chuck to grip the drill, positioning or aligning the drill in relation to the drill bit holding mechanism and to a rotary grinding stone, advancing the drill bit towards a grindstone, retracting the re-pointed drill bit from the grindstone and removing the re-pointed drill bit. Because of all of the aforementioned operations, an operator can usually operate only a single drill bit grinding apparatus at a time. Thus, even an experienced operator can typically re-point no more than about 800 to 1,000 drill bits over an eight-hour work shift Therefore, there has been a strong demand for an automated drill bit re-pointing apparatus that has a higher throughput rate than existing re-pointing apparatuses, and which may be operated by less than highly skilled personnel. Despite a widespread need for an improved drill bit re-pointing apparatus, various difficulties have prevented the development of such an apparatus. The present invention was conceived of to provide an improved, automatic drill bit re-pointing apparatus in which functions performed manually in prior art devices are largely automated. 
     OBJECTS OF THE INVENTION 
     An object of the present invention is to provide an automatic apparatus for sharpening or re-pointing twist drill bits. 
     Another object of the invention is to provide a drill bit re-pointing apparatus which includes means for automatically aligning a drill bit with respect to a grinding wheel. 
     Another object of the invention is to provide a drill bit re-pointing apparatus having a drill bit holder mechanism which facilitates attachment of the drill bit to the apparatus for grinding, and removal of the bit upon completion of grinding. 
     Another object of the invention is to provide a drill bit re-pointing apparatus having a drill bit holder which incorporates means for rotating the bit about its longitudinal axis to a desired phase angle to orient the fluted, front cutting portion of the bit to a desired disposition relative to a grinding wheel. 
     Another object of the invention is to provide a drill bit re-pointing apparatus having fluted portion support means translatable transversely or perpendicularly relative to the longitudinal axis of the bit, between a position contacting the fluted portion of drill bits of various diameters and a non-contacting position. 
     Another object of the invention is to provide a drill bit re-pointing apparatus having a drill bit holder mechanism which includes means for axially advancing a drill bit to position the point of the bit at a desired extension distance from the holder mechanism. 
     Another object of the invention is to provide a drill bit re-pointing apparatus which includes means for aligning the phase angle and longitudinal protrusion or extension of a drill bit tip relative to an optical alignment device at a first, load/unload station, rotating the drill bit holder mechanism to second, grinding station where drill bit grinding stones grind the properly phased and extended drill bit, and rotating the drill bit holder back to the first load/unload station to permit the re-pointed drill bit to be removed from the apparatus. 
     Another object of the invention is to provide a drill bit re-pointing apparatus which includes a drill bit holder which has a pivotable shank retainer which may be pivoted upwards to allow the shank of a drill bit to be placed on a pair of phase-controlling roller wheels, and which may be pivoted downwardly to retain the shank in rotatable contact with the roller wheels. 
     Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims. 
     It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, we do not intend that the scope of our exclusive rights and privileges in the invention be limited to details of the embodiments described. We do intend that equivalents, adaptations and modifications of the invention reasonably inferable from the description contained herein be included within the scope of the invention as defined by the appended claims. 
     SUMMARY OF THE INVENTION 
     Briefly stated, the present invention comprehends an apparatus for sharpening or re-pointing twist drill bits, in which functions required in the re-pointing process are largely automated. 
     An automatic drill bit re-pointing apparatus according to the present invention includes a drill bit holder mechanism having a rear, shank holder structure and a front, fluted holder structure which is actuable from a lowered, rear non-contacting position to a raised position contacting and supporting the fluted front portion of drill bits of various diameters. The drill bit holder mechanism includes a motor-driven shank retainer which is pivotable upwardly to a first position allowing placement of a drill bit in the apparatus, and removal of the bit after it has been re-pointed, and pivotable downwards to a second position bearirg against the shank of the drill bit to thereby secure the bit in the holder mechanism. The drill bit holder mechanism also includes a pair of laterally adjacent, “phase control” rollers which support the lower portion of a drill bit shank, the rollers being motor driven to permit rotating the bit about its longitudinal axis to a particular orientation or phase angle of the cutting lips of the fluted front cutting portion of the bit. A motor-driven lead screw in the drill bit holder mechanism pushes against the rear shank face of a drill bit in the holder mechanism to advance the drill bit axially with respect to the phase control rollers to a desired protrusion length or extension distance from the holder mechanism. 
     According to the present invention, the drill bit holder mechanism is pivotably mounted on a spindle rotatable by means of a connecting link coupled to a station position linear actuator cylinder from a first, load/unload station position to a second, grinding station position. At the load/unload station is located an optical alignment apparatus including an optical imaging unit that has an objective lens longitudinally aligned with and spaced outwards from the tip or point of a drill bit held in the drill bit holder mechanism. The optical imaging unit includes a CCD camera, on the focal plane of which is formed an image of the tip of the drill bit. The image is displayed on a monitor and also transmitted to an optical pattern recognition computer which outputs command signals to the phase control roller drive motor that rotates the bit to a desired phase angle or orientation suitable for contacting grinding wheels at a grinding station. 
     The optical alignment apparatus also includes an electro-optical drill bit point extension sensor located between the optical imaging apparatus and the drill bit holder mechanism. Output signals from the extension sensor drive the lead screw motor to advance the drill bit axially in the holder to a pre-determined longitudinal extension distance therefrom. 
     When the drill bit phase angle and extension have been automatically adjusted as described above, the station position actuator is energized to pivot the drill bit holder mechanism from the first, load/unload station position to the second, grinding station position at which is located a plurality of rotating grinding stones which sequentially sharpen various surfaces of the drill bit, including the chisel point and lips or cutting edges of the drill bit flutes. During the sharpening process, a controller device inputs command signals to the phase rotating rollers which rotate the bit at a predetermined rate from its initial position adjusted at the load/unload station. Upon completion of the sharpening process, the bit holder mechanism is pivotably rotated back to the first, loadlunload station. Then, the shank retainer motor is operated to pivot the shank retainer away from the re-pointed drill bit, allowing the latter to be removed and replaced with another bit to be re-pointed. By utilizing a robotic arm or similar device to load and unload drill bits from the apparatus, drill bits may be re-pointed completely automatically. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 ( 1 ) is a partly sectional upper plan view of a drill bit holder mechanism comprising part of an automatic drill bit re-pointing method and apparatus according to the present invention. 
     FIG.  1 ( 2 ) is a partly sectional side elevation view of the mechanism of FIG.  1 ( 1 ). 
     FIG. 2 is a side elevation view of an automatic drill bit re-pointing apparatus according to the present invention. 
     FIG. 3 is a fragmentary side elevation view of the apparatus of FIG. 2 on a somewhat enlarged scale, and showing the drill bit holder mechanism thereof pivoted from a first, load/unload/align station position indicated by solid lines, to a second, grinding station position indicated by phantom lines. 
     FIG. 4 is a fragmentary front elevation view of the drill bit holder mechanism of FIG. 1, showing details of a blade receiver portion of the mechanism used to support the front, fluted blade portion of a drill bit. 
     FIG. 5 is a view similar to that of FIG. 4, showing an alternate embodiment of a blade receiver. 
     FIG. 6 is a partly sectional side elevation view of the mechanism of FIG.  1 ( 1 ), but showing sections removed in addition to those removed in FIG.  1 ( 2 ). 
     FIG. 7 is a fragmentary front sectional view of the mechanism of FIG.  1 ( 1 ), showing details of the phase control device thereof. 
     FIG. 8 is a view similar to that of FIG. 7, but showing a first variation of the phase control device thereof. 
     FIG. 9 is a view similar to that of FIG. 7, but showing a second variation of the phase control device thereof. 
     FIG. 10 is a fragmentary side elevation view of the apparatus of FIG. 2, showing the relative arrangement of an optical alignment apparatus and sharpening unit thereof. 
     FIG. 11 is a front elevation view of the optical alignment apparatus portion of the re-pointing apparatus shown in FIG.  2 . 
     FIG. 12 is a front elevation of a drill bit tip as viewed on a monitor connected to the optical alignment apparatus of FIGS. 2 and 11. 
     FIG. 13 is a fragmentary upper plan view of a modification of the apparatus of FIG. 1, showing a modified shank retainer thereof pivoted upwards to permit a drill bit to be loaded or unloaded from the apparatus. 
     FIG. 14 is an oblique view of the structure of FIG.  13 . 
     FIG. 15 is a side elevation view of the structure of FIG.  14   
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1-15 illustrate various features of an automatic drill bit re-pointing apparatus according to the present invention. 
     Referring first to FIG. 2, an automatic drill bit re-pointing apparatus  10  according to the present invention may be seen to include a support structure  34  to which is pivotably attached a drill bit holder mechanism  12 . Automatic drill bit re-pointing apparatus  10  also includes an optical alignment apparatus  30  fastened to an optical bench  36 , which is in turn fastened to support structure  34  of the apparatus. Optical alignment apparatus  30  includes a telescope  32  that images the point or tip of drill bit  18  on the focal plane of a CCD camera  38 , for ascertaining the angular orientation or phase of the cutting edges or lips of a drill bit held in holder mechanism  12 . Apparatus  30  also includes an optical tip position sensor  40  for ascertaining the protrusion distance longitudinal extension of the drill bit tip relative to drill bit holder mechanism  12 . 
     As shown in sold lines in FIG. 2, drill bit holder mechanism  12  of automatic drill bit re-pointing apparatus  10  is located at a first, load/unload/align station position at which drill bits may be loaded or attached to the drill bit holder mechanism and aligned properly by means of optical alignment apparatus  30 , in a manner to be described in detail below. Then, drill bit holder mechanism  12  is pivoted to a second, sharpening station location indicated by dashed lines, by a linear actuator  16  coupled by a coupling link  26  to a pivot pin or spindle  22 . At the sharpening station, the drill bit is contacted by grinding wheels of a sharpening or grinding unit  14 . Upon completion of the grinding or re-pointing process, drill bit holder mechanism  12  is pivoted back to the first, load/unload/align station by operation of linear actuator  16 . Here the re-pointed drill bit may be removed and replaced by another bit to be re-pointed. 
     Referring now to FIGS.  1 ( 1 ) and  1 ( 2 ), it may be seen that drill bit holder mechanism  12  includes a generally flat, longitudinally elongated base plate  20 . A pivot pin or spindle  22  disposed laterally near the rear edge wall of the plate is secured to the underside of the plate. As shown in FIG. 2, opposite lateral ends of spindle  22  are rotatably secured in a pair of opposed bushings  24  fastened to apparatus support structure  34 . 
     Referring still to FIGS.  1 ( 1 ) and  1 ( 2 ), it may be seen that drill bit holder mechanism  12  of apparatus  10  includes a motor mounting plate  42  which protrudes perpendicularly upwards from base plate  20  of the mechanism. Attached to motor mounting plate  42  is a drill bit tip axial position controller motor  44  which powers a lead screw-type linear tip position actuator mechanism used to advance drill bit  18  in the direction of its longitudinal axis. Also attached to motor mounting plate  42  is a phase controller motor  46  which powers a rotary flute orientation actuator used to rotate drill bit  18  around its longitudinal axis. As shown in FIG.  1 ( 1 ), drill bit holder mechanism  12  also includes a linear shank holder actuator cylinder  48  which is preferably a pneumatic cylinder, and has a piston rod  76  which is longitudinally slidably disposed through motor mounting plate  42 . The remaining structural components and functions of the three aforementioned actuators are described in detail below. 
     Referring again to FIGS.  1 ( 1 ) and  1 ( 2 ), it may be seen that drill bit holder mechanism  12  includes a drill bit shank holder block  50  which protrudes perpendicularly upwards from upper surface  21  of base plate  20 . Shank holder block  50  is located longitudinally forward of actuator motor mounting plate  20 , and rearward of the front transverse edge wall of base plate  20 . Referring to FIGS. 6 and 7 in addition to FIGS.  1 ( 1 ) and  1 ( 2 ), it may be seen that shank holder block  50  supports a pair of parallel, laterally spaced apart and aligned spindles  52  which are rotatably supported by bearing (not shown) within the block, and which protrude longitudinally forward from the front surface of the block. Near the front end of each rotatable spindle  52  is attached a circular disk-shaped roller  154  having an outer circumferential surface made of rubber. As may be seen best by referring to FIG. 7, the inner facing surface of rollers  54  are spaced very slightly apart from one another, thus forming an arcuately curved, generally V-shaped recess  55  between the upper portion of the rollers which may receive the shank of a drill bit  18 . As shown in FIGS. 1 and 2, drill bit  18  is placed on rollers  54  with the shank of the bit protruding rearward towards shank holder block  50 . 
     Referring now to FIG. 4 in addition to FIGS. 1 and 2, it may be seen that drill bit holder mechanism  12  includes a front fluted portion receiver  56  for supporting the front fluted portion of a drill bit  18 . Fluted portion receiver  56  includes an arm  57  which protrudes obliquely upwardly from a support block  58 , and has at the upper end thereof a fluted portion support flange  59  adapted to support the lower surface of the front, fluted cutting portion of a drill bit  18  held in holder mechanism  12 . Support block  58  is attached to the upper end of a vertically disposed fluted portion receiver actuator  60 , which is in turn fastened to support plate  20 . By energizing actuator  60 , fluted portion receiver  56  may be moved up and down, as indicated by arrows  62  in FIG. 4, to support the front fluted portion of drill bits of various diameters. 
     FIG. 5 illustrates an alternate mechanism  65  for raising and lowering fluted portion receiver  56 . Alternate mechanism  56  includes a pivot arm  64  which is attached at the upper end thereof to fluted portion receiver  56 . A side of the lower end of pivot arm  64  bear&#39;s tangentially against the outer surface of a cam  66  driven by a motor (not shown). Thus, when the cam is driven by the motor, pivot arm  64  pivots in the direction indicated by arrows  68  in FIG. 5, raising or lowering fluted portion receiver  56 . 
     Referring again to FIG.  1 ( 2 ), it may be seen that drill bit holder mechanism  12  includes a finger-like shank retainer  70 . As shown by arrows  74  in FIG.  1 ( 2 ), shank retainer  70  may be pivoted in a vertical plane between an upper, non-contacting position allowing loading and unloading of a drill bit  18  into drill bit holder mechanism  12 , and a lower position in which the “finger tip” of the shank retainer bears against the upper surface of the shank of a drill bit  18 , thus pressing the shank against phase controller rollers  54 , (see FIG.  1 -( 1 )), and thereby securing the drill bit in the holder. Drill bit holder mechanism  12  includes components described below which cooperate with shank retainer actuator cylinder  48  to pivot shank retainer  70  between an upper, load/unload position to a lower, shank retaining position. 
     Thus, as shown in FIG.  1 -( 1 ), a piston rod  76  protrudes forward from actuator cylinder  48  through motor mounting plate  42 , and is coupled at the front end thereof through a first crank arm-link structure  82  to an intermediate longitudinal location of an operating spindle or first pivot shaft  80 , which is rotatably mounted about its longitudinal axis relative to drill bit shank retainer block  50 . First pivot shaft  80  in turn is coupled at an inner longitudinal location thereof, nearer shank retainer block  50 , by a second, inner crank arm-link structure  82  to a first, left side longitudinal support arm  72 L for shank retainer finger  70 . Pivot arm  72 L and a counterpart support arm  72 R are disposed parallel to left and right sides of shank retainer support block  50 , respectively, and are fastened to opposite lateral ends of a second pivot rod  73  that is transversely disposed through the shank retainer block, and rotatably supported therein. Attached to the front ends of arms  72 L,  72 R is a transversely disposed cross arm  85 . Shank retainer finger  70  is fastened to the center of cross arm  85 . Therefore, when shank retainer actuator cylinder  48  is energized, coupling link structure  78  causes operating spindle  80  to rotate, rotational motion of which is transferred through coupling link structure  82  to the rear end of left longitudinal shank retainer support arm  72 L. Downward pivotal motion of the rear end of shank retainer longitudinal support arm  72 L causes the longitudinal support arm to pivot upwards about pivot rod axle  73 , which in turn causes the front end of support arm  72 L, cross arm  85  and shank retainer finger  70  to pivot upwardly away from the shank of drill bit  18 . Conversely, actuation of linear actuator cylinder  48  in the opposite direction causes shank retainer finger  70  to pivot downwardly and bear against the shank of drill bit  18 . 
     FIG. 6 illustrates the structure and function of components which cooperate with drill bit tip axial position controller motor  44  to extend the point of a drill bit  18  to a desired protrusion length or extension distance relative to fluted portion receiver  56 . As shown in FIG. 6, axial tip position controller motor  44  has a shaft  89  which protrudes forward through actuator motor mounting plate  42 , the shaft having a drive gear  84  pinned to the front end of the shaft. Drive gear  84  is a spur gear having longitudinally disposed teeth that slidably mesh with teeth of a driven gear  88  pinned to the rear end of a spindle  86 . Spindle  86  has an enlarged diameter. longitudinally centrally located mid-section  90  which has a helically threaded outer surface. Threaded mid-section  90  of spindle  86  is threadingly engaged within an internally threaded bore  91  disposed longitudinally through drill bit shank holder block  50 . Thus, when motor  44  turns drive gear  84 , driven gear  88  threadingly advances or retracts mid-section  90  Of spindle  86  in threaded bore  91 , depending upon whether motor shaft  89  rotates clockwise or counterclockwise. Since gears  84  and  88  are spur gears, relative longitudinal sliding movement between the gears may occur while torque is transmitted through the meshed gears to spindle  86 . 
     As shown in FIG. 6, bore  91  through shank holder block  50  is coaxially aligned with a drill bit  18  supported on phase control rollers  54 . When a drill bit  18  is initially loaded into drill bit holder mechanism  12 , motor  44  is commanded to fully retract spindle  86  in bore  91 , allowing the shank of the bit to be inserted some distance into bore  91  until the rear face of the shank abuts the front face of spindle  86 . With this arrangement, motor  44  may be powered for a duration sufficient to advance spindle  86  and bit  18  axially forward until the point  132  of the bit protrudes a desired distance from fluted portion receiver  56 . 
     FIG. 6 also illustrates components of holder mechanism  72  which cooperate with phase controller motor  46  to rotate a drill bit  18  about its longitudinal axis to a predetermined angular orientation of the cutting lips of the drill bit. 
     Thus, as shown in FIG. 6, phase controller motor  46  has a shaft  97  which protrudes forward through actuator motor mounting plate  42 , the shaft having a drive gear  92  pinned to the front end of the shaft. Drive gear  92  is a spur gear having longitudinally disposed teeth that mesh with teeth of a driven gear  96  pinned to the rear end of an axle shaft  52 . Axle shaft  52  is rotatably supported in drill bit shank holder block  50 , and protrudes forward through the drill bit shank holder block, beyond the front wall surface thereof. As shown in FIG. 7, a driver roller  98  is pinned to the front end of axle shaft  52 , and tangentially contacts a pair of adjacent phase control rollers  54 . Thus, when axle shaft  52  and driver roller  98  are rotated in a clockwise direction by phase controller motor  46 , contact of the driver roller with phase control rollers  54  causes the latter to rotate in the opposite, i.e., counterclockwise direction. Also, tangential contact between phase control rollers  54  and the shank of a drill bit  18  pressed downwardly into recess  55  between the rollers causes the shank to rotate in a direction opposite to that of the rollers, i.e., in a clockwise sense. Thus, drill bit  18  may be rotated in a clockwise or counterclockwise direction to a desired angular orientation by electrically powering phase controller motor  46  to rotate in a clockwise or counterclockwise direction. 
     FIG. 8 illustrates a first variation of the phase control device depicted in FIG.  7  and described above. In this first variation, the shank of a drill bit  18  is pressed into contact with a pair of adjacent idler rollers  102  made of a metal or the like. The upper surface of drill bit shank  18  is pressed against by a friction pad  108  disposed laterally on the underside of a laterally disposed, phase adjusting drive arm  106  movable in a lateral direction by a linear actuator (not shown). When drive arm  106  is moved forward to the left or back to the right, as shown by the arrows  104 ; drill bit  18  is caused to rotate in a counterclockwise or clockwise sense, respectively. 
     FIG. 9 illustrates a second variation of a phase control device, which is substantially similar in structure and function to the device depicted in FIG.  8  and described above. However, in the device depicted in FIG. 9, idler rollers  102  are replaced by a block  110  having in the upper surface thereof a V-shaped groove for rotatably receiving the shank of a drill bit  18 . 
     FIG. 10 illustrates structural details of sharpening unit  14 . As shown in FIG. 10, sharpening unit  14  has a primary rotating sharpening stone  112  which sharpens a first tip surface of a drill bit  18 , and a secondary sharpening stone  114  which sharpens a second tip surface. Sharpening stones  112 ,  114  are installed on rotary drive motors  116 ,  118 , respectively, the spin axes of which are inclined at different angles with respect to the longitudinal axis of a drill bit  18  to an orientation suitable for sharpening the first and second surfaces of the drill bit tip. In addition, sharpening stones  112 ,  114  are arranged on a table  120  which is made to tilt against the drill bit  18 , with a traversing structure (not shown) which moves sharpening stone driver motors  1   16 ,  11   8 , with respect to the table  120 , as shown by arrows  122 . 
     The structure and function of optical alignment apparatus  30  of drill bit re-pointing apparatus  10 , may be best understood by referring to FIGS. 2,  11  and  12 . 
     As shown in FIG. 11, optical imaging unit  31  of optical alignment apparatus  30  includes an annular light source  126  which fits coaxially over the objective lens tube  124  of a telescope tube  32 . An annular pattern of light rays directed forward from light source  126  is effective in illuminating tip of drill bit  18 . 
     Tip position sensor  40  of apparatus  30  includes a photo detector  128  which protrudes radially outwards from optical bench  36 , near the front end of the optical bench. Photo detector  128  is axially offset inwardly from the optical axis of telescope tube  32 , and transversely aligned with a plane spaced forward of objective lens  124 . Optical tip position sensor  40  also includes a light source  130  transversely aligned with photo detector  128 , and radially offset outwardly from the optical axis of telescope tube  32 . Light source  130  illuminates sensor  128  with a transversely disposed beam of light. Photo detector  128  outputs a detection signal indicative of the axial extension distance of the point of a drill bit  18  relative to sensor  40 , the detection signal being used to command axial position motor  44  to advance drill bit  18  to a pre-determined extension position forward of fluted portion receiver  56 . 
     Operation of automatic drill bit re-pointing apparatus  10  is as follows: 
     First, as shown in FIG. 2, a drill bit  18  to be re-pointed is loaded into drill bit holding apparatus  12 , with the holding apparatus located at the load/unload/alignment station position shown at the left-hand side of FIG.  2 . Drill bit  18  is loaded by placing the shank of the bit onto phase controller rollers  54 , and pushing the bit rearward into bore  91  of drill bit shank holder block  55  sufficiently far for the rear face of the drill bit shank to contact the front face of axial position controller spindle  86 , which has been retracted in bore  91  by an initialization command signal issued to axial drive motor  44  from an electronic controller, such as a computer (not shown). Drill bit  18  is loaded into holder apparatus  12  by any convenient means, such as by hand, or preferably by an automatic handling apparatus such as a robotic arm. As shown in FIGS.  1 -( 1 ) and  1 -( 2 ), drill bit  18  is positioned in holder apparatus  12  with the front, fluted portion of the bit supported on fluted portion receiver  56 . After drill bit  18  has been thus positioned in drill bit holder apparatus  12 , shank retainer actuator cylinder  48  is energized, causing shank retainer finger  70  to pivot downwardly against the upper surface of the shank of drill bit  18 , pressing the lower surface of the shank into secure contact with phase controller rollers  54 , as shown in FIG.  1 -( 2 ). 
     With a drill bit  18  installed in drill bit holder apparatus  12  in the manner described above, the control computer issues a command signal which causes axial position drive motor  44  to rotate, causing lead screw spindle  86  to advance in bore  91  of shank holder support block  50 . Spindle  86  pushes drill bit  18  axially forward until point  132  of the bit extends to within a predetermined distance forward of objective lens  124  of optical alignment sensor  30 . At the predetermined position, axial point position sensor photo detector  128  produces a detection signal which commands cessation of drive current to drive motor  44 , thus maintaining the point of drill bit  18  at the predetermined axial extension. 
     When point  132  of drill bit  18  has been positioned at a desired axial extension beyond fluted portion receiver  56 , as determined by point position sensor  40 , telescope  32  of optical imaging unit  31  forms an image of the front fluted portion of drill bit  18  on the focal plane of CCD camera  38 , as shown in FIG.  12 . If the center of drill bit chisel point  132  is not at a pre-determined, centered position in the field of view of telescope  32 , such as the intersection of the horizontal and vertical cross hairs shown in monitor image  34  of FIG. 12, pattern recognition logic within the computer controller issues a command signal to fluted portion receiver actuator  60  to raise fluted portion receiver  56 , thus elevating chisel tip  132  to the pre-determined alignment position. Since, in the preferred embodiment, phase control rollers  54 , of bore  91 , and shank retainer finger  70  are arranged so that the front end of drill bit 18 tilts downward slightly, as viewed in FIG.  1  -( 1 ), it is only necessary to elevate fluted portion receiver  56  to vertically align drill bit chisel point  132  in the monitor image  134 . 
     With chisel point  132  of drill bit  18  centered at a pre-determined position in monitor image  134 , as described above, pattern recognition logic within the computer controller determines whether the lips or cutting edges  140  of the drill bit are oriented at a predetermined phase angle θ (theta) with respect to the horizontal center line of the image. If the measured phase angle differs from the pre-determined value, the computer controller issues a command signal to phase controller motor  46  to rotate drill bit  18  to the pre-determined phase angle. 
     After drill bit  18  has been precisely aligned relative to drill bit holder mechanism  12  using optical alignment apparatus  30 , as described above, the computer controller issues a command signal to station position actuator cylinder  16 . This action causes drill bit holder mechanism  12  to pivot downwardly from the first, load/unload/align station position shown in FIG. 2, to a horizontal disposition in which drill bit  18  is presented to sharpening station  14 . Then, the computer controller issues command signals which cause first and second rotating grinding stone motors  116  and  118  to be moved by the traversing structure to translate the grinding stone motors in a pre-determined pattern, with first and second grinding stones sequentially contacting drill bit  18 . During this operation, the computer controller issues drive signals to phase controller motor  46  which rotate drill bit  18  during the sharpening process. 
     After completion of the sharpening process, the computer controller issues a command signal to station position actuator  16  which causes drill bit holder mechanism  12  to pivot upwardly from the sharpening station position adjacent sharpening unit  14  to the load/unload/align station position adjacent optical alignment apparatus  30 . Here an image of sharpened drill bit  18  is formed on the focal plane of CCD camera  38 . The image is conveyed to the computer controller, wherein pattern recognition logic determines whether the shape of the sharpened drill bit falls within pre-determined acceptance parameters, in which case a PASS status signal is issued, or if outside the limits, a FAIL status signal is issued. After the PASS/FAIL test determination, the computer controller causes a command signal to issue to shank retainer actuator cylinder  48  which causes shank retainer finger  70  to pivot upwardly to an unload position, thus allowing the re-pointed drill bit to be removed and replaced with another bit to be re-pointed. 
     As explained above, the design of the drill bit holder mechanism of the automatic drill bit re-pointing apparatus according to the present invention facilitates loading and unloading drill bits from the apparatus. In addition, because the holder includes a lead screw mechanism for axially moving the drill bit to a pre-determined axial position, a cutting portion receiver actuator for transversely moving the drill bit point to a pre-determined height, and a phase controller mechanism for rotating the bit to a pre-determined initial phase angle of the cutting lips of the drill bit, and rotating the bit from the initial phase angle during grinding, sharpening of drill bits can be performed fully automatically with the apparatus according to the present invention. 
     FIGS. 13-15 illustrate a preferred modification of the apparatus of FIGS.  1 -( 1 ) and  1 -( 2 ), which include a modification of the shank retainer  70  shown therein and described above. 
     As shown in FIGS. 13-15, modified shank retainer  100 , rather than having a finger-like shape as depicted in FIG.  1 -( 2 ), comprises a cylindrically-shaped bushing  101  which protrudes from the front wall  103  surface of a plate-like cross arm  102 . Bushing  101  is rotatably supported by an internal roller bearing assembly  104  which is fastened to front surface  103  of cross arm  102 . With cross arm  102  pivoted downwardly as shown in FIGS. 14 and 15, bushing  101  tangentially contacts the shank of a drill bit  18 . With this arrangement, modified shank retainer  100  may exert a substantial normal force against the shank of drill bit  18 , while still allowing phase control rollers  54  to readily rotate the drill bit about its longitudinal axis.