Abstract:
A vibration damper for a drill tube of a hole machining apparatus includes a closed loop bi-directional adjustment mechanism, which operates from a single side of the damper. The closed loop mechanism ensures that the position of the clamping sleeve has a one-to-one relationship with the adjustment mechanism, which enables controlled adjustment of the clamping force to be performed. Locating the adjustment mechanism at one side of the clamping sleeve facilitates re-tooling, e.g. replacing the clamping sleeve if a larger diameter drill tube is to be used.

Description:
RELATED APPLICATION DATA 
       [0001]    This application claims priority under 35 U.S.C. §119 to EP Patent Application No.12197190.7 filed on Dec. 13, 2013, which the entirety thereof is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a vibration damper for a rotating drill tube or boring bar in hole machining apparatus, such as for deep hole drilling. 
       BACKGROUND TO THE INVENTION 
       [0003]    It is known to damp or suppress vibrations of a drill tube which occur during hole machining by bringing an independently rotatable mass into frictional engagement with the rotating drill tube. Conventionally, the rotatable mass is an annular member mounted around the drill tube. The frictional engagement between the drill tube and annular member is provided by a tapering (i.e. frustoconical) clamping sleeve. A cooperating tapering collet can be drawn on and off the clamping sleeve through the movement of adjustment members located at each end of the clamping sleeve along the axis of the drill tube. 
         [0004]    The adjustment members of conventional vibration dampers can be adjusted manually or via hydraulic actuators. In a known manual device, the adjustment member is threaded in a tapped bore of the damper housing (sometimes referred to as the damper carriage). Thus, a first adjustment member may be screwed into the damper housing to force the collet down the tapering clamping sleeve, which consequently applies a radial force on the drill tube. The damper may include one or more springs arranged to push the collet back up the taper upon release. These springs may be primed once the collet is in place by adjustment the second adjustment member at the opposite side of the clamping sleeve. Thus, upon screwing the first adjustment member out of the damper housing to release the clamping, the collet is forced up the taper by springs. 
         [0005]    In practice, the desired clamping force is set through fine adjustment of the first adjustment member, which is fixed by closing the second adjustment member. A disadvantage of this arrangement is that if the springs fail to release the collet, e.g. if they seize up during use, damage can occur when the damper housing is moved. 
         [0006]    The known hydraulically actuated device works in a similar way, in that the collet can be forced on to the clamping sleeve through appropriate adjustment of the first adjustment member via an hydraulic actuating force, and in that springs are provided to release the mechanism. The hydraulic system allows the damper to be actuated from outside the machine, but does not provide as much control as the manual device. Moreover, the presence of springs causes the same disadvantages as for the manual device. 
         [0007]    U.S. Pat. No. 4,305,264 discloses a vibration damping device in which a clamping sleeve is movable along the axis of a drill tube to provide a frictional connection to a flywheel. The clamping sleeve is sandwiched between two threaded adjustment members, which are movable simultaneously along the axis of the drill tube. 
       SUMMARY OF THE INVENTION 
       [0008]    One aspect of the disclosure provides a bi-directional adjustment mechanism in which a drive member engages in a self-locking manner with an adjustment element of a vibration damper. The self-locking engagement may enable accurate positioning of the clamping sleeve in the vibration damper. The bi-directional nature of the adjustment mechanism may allow it to operate from only a single side of the damper. The self-locking engagement may further form part of a closed loop mechanism which ensures that the position of the clamping sleeve has a one-to-one relationship with the adjustment mechanism, i.e. the position of the drive member on the adjustment element, which enables fine adjustment of the clamping force to be performed. 
         [0009]    According to an embodiment, there is provided a vibration damper for a drill tube of a hole machining apparatus, the vibration damper includes a damper carriage for mounting around the drill tube; an inertial mass rotatably mounted in the damper carriage; a clamping sleeve mounted in the damper carriage, the clamping sleeve having a bore for receiving the drill tube and being axially movable relative to the damper carriage to provide frictional engagement between the drill tube and inertial mass; an adjustment element connected to the clamping sleeve to move axially with the clamping sleeve and to rotate freely relative to the clamping sleeve; and a bi-directional drive mechanism arranged to drive the clamping sleeve forwards and backwards along its axis via the adjustment element, wherein the bi-directional drive mechanism includes a drive member in self-locking engagement with the adjustment element. 
         [0010]    The axial position of the inertial mass in the damper carriage may be fixed. As explained above, the self-locking engagement between the adjustment element and the drive member may form a closed loop mechanism. If the axial position of the inertial mass is fixed, the effect of the closed loop mechanism is to permit precise control of the axial position of the clamping sleeve relative to the inertial mass. Since the relative axial position of the clamping sleeve and inertial mass sets the compression force on the drill tube, the compression force can thus be controlled accurately in an automated manner. 
         [0011]    The clamping sleeve may be tapered such that axial movement thereof relative to the inertial mass causes radial compression or expansion of the clamping sleeve to press against (clamp on to) or release the drill tube. The clamping sleeve may comprise one or more axial slits to facilitate this radial compression and expansion. 
         [0012]    The adjustment element may be connected to the clamping sleeve at only one axial end thereof. Thus, the adjustment element may operate to both push and pull the clamping sleeve along its axis. This arrangement may reduce the chances of the clamping sleeve becoming stuck in an engaged position. Locating the adjustment element at one side of the clamping sleeve facilitates re-tooling, e.g. replacing the clamping sleeve if a larger diameter drill tube is to be used. 
         [0013]    The adjustment element may be connected to the clamping sleeve via one or more bearings, e.g. axial bearings, to permit the clamping sleeve to rotate with the inertial mass (and drill tube) relative to the adjustment element. The clamping sleeve may include a support ring at the axial end opposite the adjustment element. The support ring and clamping sleeve may be bolted to a bearing housing containing said one or more bearings by a plurality of bolts extending through the body of the clamping sleeve. 
         [0014]    The connection between the adjustment element and the clamping sleeve may comprise an annular bearing housing having a first bearing seat for receiving a first axial bearing and a second bearing seat for receiving a second axial bearing, wherein the second bearing seat faces in the opposite direction to the first bearing seat, and the adjustment element comprises a radial flange disposed between the first and second bearing seats. 
         [0015]    In one embodiment, the adjustment element may comprise a threaded sleeve extending in an axial direction. The threaded sleeve may be in threaded engagement with a drive transfer ring mounted on the damper carriage, whereby rotation of the adjustment element in either direction is transformed into simultaneous axial movement of the threaded sleeve into or out of the damper carriage. 
         [0016]    The bi-directional drive mechanism may comprise a worm drive arranged to rotate the adjustment element. The worm drive may comprises a worm gear mounted to rotate with the threaded sleeve, and a worm driven by a suitable rotary drive arranged to apply a torque thereto. Other drive mechanisms may be used, e.g. a pulley to rotate a drive nut that is in threaded engagement with the adjustment element. 
         [0017]    The bi-directional drive mechanism may be controllable via a computer numerical control (CNC) operating system, e.g. via the same CNC machine that operates the hole machining apparatus. The bi-directional drive mechanism may also be operable manually, e.g. as a back up or safety measure. 
         [0018]    The CNC operating system may be programmable to set a desired clamping force in the vibration damper, e.g. via suitable calibration to a measurable parameter associated with the rotary drive. For example, the torque applied by the rotary drive may be detected by a suitable sensor. The closed loop nature of the bi-directional device allows the torque transmitted to be calibrated with the compression force between the clamping sleeve and drill tube. 
         [0019]    One advantage of automated control of the compression force, is that it allows remote adjustment of the clamping sleeve. This may be useful where it is desirable to allow some slipping between the drill tube and clamping sleeve, e.g. when the vibration damper reaches the end of its track on the hole machining apparatus. Adjustment may be made on the fly, e.g. through the CNC operating system interface. Alternatively or additionally, a compression profile may be pre-programmed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    An embodiment of the invention is discussed in detail below with reference to the accompanying drawings, in which: 
           [0021]      FIG. 1  is an exploded perspective view of a vibration damper that is an embodiment of the invention. 
           [0022]      FIG. 2A  is a side view of the vibration damper of  FIG. 1  in an assembled state. 
           [0023]      FIG. 2B  is a rear view of the vibration damper of  FIG. 1  in an assembled state. 
           [0024]      FIG. 3  is a cross-sectional view through the line F-F in  FIG. 2B . 
           [0025]      FIG. 4  is a schematic view of a hole machining apparatus in which the vibration damper of the invention may be used. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows the components of a vibration damper according one embodiment. The vibration damper includes an annular damper carriage  10  for mounting on a hole machining apparatus. The damper carriage  10  may be mounted in a steady-rest (not shown) e.g. using location connector  54 . As is conventional, the steady-rest is slidably mounted on the machine bed of the hole machining apparatus. The damper carriage  10  and all the other annular components of the damper include a central aperture or bore  60  (see  FIG. 2B ) for receiving the drill tube (not shown) of the hole machining apparatus. References herein to an axial direction refer to a direction along an axis extending through the central aperture, i.e. in line with the drill tube. 
         [0027]    The damper carriage  10  houses components which are arranged to damp vibrations of the drill tube by connecting an additional rotatable mass to it. The damper carriage  10  thus contains an inertial mass  12 , which is rotatably mounted therein on radial bearings  13 ,  14  at each axial end thereof (see  FIG. 3 ). The position of the inertial mass  12  is fixed in an axial sense, i.e. it cannot move in the axial direction, by annular axial end plates  15   a,    15   b,  which are mounted on each end of the bore through the damper carriage  10 . 
         [0028]    As shown most clearly in  FIG. 3 , the inertial mass  12  has a bore extending through it. The surface of the bore is partitioned into two sections: a conically tapering surface at one axial end, and a widened portion at the other axial end. The inertial mass  12  contains within the bore a clamping sleeve  24 , an adjustment element  22  and a bearing housing containing two axial bearings  20   a,    20   b.  The bearing housing is received in the widened portion of the bore. The clamping sleeve  24  is received in the conically tapering part of the bore. The adjustment element  22  is connect to the clamping sleeve  24  via the axial bearings  20   a,    20   b  and extends in an axial direction through the bearing housing to protrude from one end of the damper carriage  10 . 
         [0029]    The bearing housing has a first housing portion  18 , which is bolted to the clamping sleeve  24  by bolts  28 , which extend axially through the clamping sleeve  24 . The bolts  28  act on a support ring  26  which spreads the attachment force around the circumference of the clamping sleeve  24 . The first housing portion  18  has a first bearing seat for receiving a first axial bearing  20   a.  The first axial bearing  20   a  is disposed between a flange on the axial end of the adjustment element  22  in the damper carriage and the first bearing seat, whereby axial movement of the adjustment element  22  in a first sense (which here is into the damper carriage, i.e. right to left in  FIG. 3 ) is transferred to axial movement of the clamping sleeve  24  in the same sense by the flange pushes on the first axial bearing  20   a.    
         [0030]    The bearing housing includes a second housing portion  16 , which is in fixed threaded engagement with the first housing portion  18 . The second housing portion  16  has a second bearing seat for receiving a second axial bearing  20   b.  The second bearing seat faces in the opposite direction to the first bearing seat. The second axial bearing  20   b  is disposed between the flange of the adjustment element  22  and the second bearing seat, on the opposite side of the flange from the first bearing seat. This arrangement means that axial movement of the adjustment element  22  in a second sense (which here is out of the damper carriage, i.e. left to right in  FIG. 3 ) is transferred to axial movement of the clamping sleeve  24  in the same sense by the flange pushing on the second axial bearing  20   b.  The first axial bearing  20   a  thus acts to transfer a “pushing” force to the clamping sleeve  24 , whereas the second axial bearing acts to transfer a “pulling” force to the clamping sleeve. 
         [0031]    The clamping sleeve  24  itself may be of a conventional split fibre cone type. It has a frustoconical shape arranged to cooperate with the conically tapering inner surface of the inertial mass  12 . Axial movement of the clamping sleeve  24  may thus draw the tapering surfaces together or apart. As the surfaces are drawn together, the clamping sleeve is compressed against the drill tube. The inertial mass  12  is thus brought into frictional engagement with the drill tube through the clamping sleeve  24 . 
         [0032]    The portion of the adjustment element  22  that extends through the bearing housing and protrudes from the damper carriage  10  comprises a tube with outer threads. These threads engage the inner threads of a guide ring  30  with is fixed, i.e. bolted, on the axial end plate  15   b  at the end of the damper carriage  10  where the adjustment element  22  protrudes. The threaded engagement between the guide ring  30  and adjustment element  22  means that any rotation of the adjustment element  22  relative to the damper carriage  10  causes a simultaneous axial displacement of the adjustment element  22  relative to the damper carriage  10  (and hence relative to the inertial mass  12 ). The threaded engagement is bi-directional, in that rotation in one sense causes axial movement into the damper carriage  10 , whereas rotation in the opposite sense causes axial movement out of the damper carriage  10 . 
         [0033]    The adjustment element  22  is received in a drive transfer ring  32 , which in this embodiment is attached (e.g. using radial screws or bolts) to the end of the adjustment element  22  that protrudes from the damper carriage. The drive transfer ring  32  is keyed connection with an annular worm gear  34  such that rotation of the worm gear  34  is transferred to rotation of the adjustment element  22 . The worm gear  34  is encased in a worm gear cover  46   a,    46   b,  which is mounted on the axial end plate  15   b  of the damper carriage  10 . 
         [0034]    The worm gear  34  is engaged with a worm  36  disposed at one side thereof, i.e. to the side of the drill tube in use. The worm  36  is rotatably mounted on a seat  50  via rotary bearing  52 . The seat  50  is mounted on the axial end plate  15   b.  The worm  36  is driven by a rotary drive  38  via a gearbox  40 . The rotary drive  38  and gearbox are supported on a bracket  44  attached to the axial end plate  15   b.  The bracket  44  includes an aperture for receiving the worm  36 . Rotation of the worm in the aperture is facilitated by a bushing  42 . The worm  36  may be protected by a cover  48 . 
         [0035]    Although the present embodiment envisages the use of a rotary drive to provide the power to rotate the worm  36 , the gearbox  40  may be arranged to permit manual operation, e.g. through the use of an appropriate crank tool. 
         [0036]      FIGS. 2A and 2B  show side and rear views respectively of the vibration damper in an assembled state. It can be appreciated from  FIG. 2A  in particular that having the drive mechanism for the vibration damper on only one side of the damper carriage  10  improves access to the interior of the carriage, e.g. from the left hand side in  FIG. 2A . 
         [0037]      FIG. 3  shows a cross-sectional view of the vibration damper. In use, the rotary drive  38  can be operated to turn the worm  36  to cause rotation of the adjustment element  22  relative to the damper carriage  10 . The threaded engagement between the adjustment element  22  and the drive transfer ring  32  transforms the rotation into an axial movement either into or out of the damper carriage  10 . The axial movement of the adjustment element  22  is transferred to the clamping sleeve  24  through the axial bearings  20   a,    20   b.  Axial movement of the clamping sleeve  24  relative to the conically tapering surface of the inertial mass  12  brings the clamping sleeve  24  into or out of frictional engagement with the drill tube. 
         [0038]    In this embodiment, the features which provide the closed loop bi-directional drive mechanism of the invention are the combination of the worm drive (worm  36  and worm gear  34 ) and threaded engagement between the adjustment element  22  and the drive transfer ring  32 . These features allow the axial position of the clamping sleeve to be known and set accurately. The axial position of the clamping sleeve relative to the inertial mass is related to the compression force applied to the drill tube. The torque required to drive the clamping sleeve to a particular axial position may thus be calibrated with the compression force achieved at that position. This arrangement can be used to enable the apparatus to set automatically, e.g. through the use of a suitably programmed CNC operating system. 
         [0039]    As mentioned above, the closed loop bi-directional drive mechanism may be implemented in other ways, e.g. by driving the adjustment element via a pulley arrangement, or other arrangement that allows accurate control over the axial displacement of the adjustment element relative to the damper carriage  10 . The closed loop mechanism ensures that the position of the clamping sleeve has one-to-one relationship with the adjustment mechanism. The position of the adjustment mechanism can be represented by any one of a number of parameters, e.g. the position of the adjustment element within the guide ring, or the angular position of the worm gear or number of rotations of the worm relative to some predetermined start position. The important thing is that unlike a conventional damper arrangement there is no other adjustable part that allows the clamping sleeve to be moved while the adjustment mechanism remains unchanged. 
         [0040]      FIG. 4  shows a hole machining apparatus  100  in which the vibration damper of the invention may be used. The hole machining apparatus  100  comprises a drill tube  104  which is driven to rotate by a suitable connector  108  and supported by a suitable bush assembly  102 . One or more vibration dampers  106  are typically mounted between the bush assembly  102  and the connector  108 . As drilling proceeds, the drill tube may move axially into the workpiece. This movement causes the connector  108  to move along the apparatus  100 . The vibration damper  106  may also move with the drill tube  104 . However, if the vibration damper  106  reaches the bush assembly  102 , it is no longer able to move with the drill tube. At this point it may be desirable to allow slipping between the drill tube and vibration damper. The present invention provide a mechanism for automatically (and remotely) altering the compression force exerted in the damper, which means slipping can be permitted in a controlled yet rapid manner. 
         [0041]    The material ejected back through the drill tube  104  from the machining process may be passed through various filters  110  and coolers  112  before being transported on a conveyor  114  to a chip centrifuge  116 .