Abstract:
A boring head ( 10 ) having a movement transmission mechanism for selectively moving a cutting insert ( 20 ) a desired amount. The movement transmission mechanism includes a rotatable member selectively radially displacing the cutting insert the desired amount in a first direction and a primary member selectively radially displacing a balancing mass ( 50 ) in a second direction opposite the first direction while also axially displacing the balancing mass. The displacement of the balancing mass in the second direction effectively counters the displacement of the cutting insert in the first direction such that rotational balance of the boring head is automatically maintained.

Description:
RELATED APPLICATION DATA 
     The present invention claim priority pursuant to 35 U.S.C. §119(a) to Brazilian Patent Application Number 1020140262466 filed Oct. 21, 2014 which is hereby incorporated by reference in its entirety. 
     FIELD 
     The present invention relates to a device for compensating masses, and particularly to a device for compensating masses in rotary boring heads used for finishing high precision bores. The present invention also relates to a rotary boring head incorporating such a mass compensating device. 
     BACKGROUND 
     In the prior art, boring heads are known of the type that are fixed on a machine tool main spindle such that there is only one single position under which the center of gravity of the movable sliding element of the tool holder and the cutting tool itself coincide with the rotating axis of the boring head. 
     It is also known in the prior art that with the displacement of the movable parts of the boring head, the center of gravity of the boring head changes its balancing position, which is normally located over the rotating axis, leading to the unbalancing of the boring head. This unbalancing action increases even more as a sliding element in the boring head to which a cutting element is coupled is radially displaced to the outside in relation to the rotating axis. 
     Owing to vibrations generated by the lack of balancing masses in the boring head, the harm caused to the precision and finishing of bores during machining have led to the addition of balancing devices to the boring heads. 
     In addition, since the bore precision is micrometric and rotation of current boring heads reaches extremely high levels, any unbalancing, even if only of a minute increment, leads to a quality loss of the machining job, because in these cases very close tolerances in the order of thousandths of a millimeter are under consideration. 
     In the prior art, an attempt has been made to overcome the unbalancing condition through the action of counterweights for mass displacement. However, it is a disadvantage that the known embodiments of such counterweights do not enable the rotary boring head to attain sufficiently high levels of graduated balancing operation adequate for each situation. 
     Additionally, known balancing systems typically require manual adjustment in order to satisfactorily balance the cutting tool which may be very time consuming, depending on the desired balancing quality. 
     Furthermore, other known balancing systems utilize numerous components machined to tight tolerances which typically utilize complex geometries. 
     Accordingly, there exists a need for improved systems for balancing rotary boring tools. 
     SUMMARY 
     Accordingly, deficiencies in the prior art are addressed by embodiments of the invention which are directed to a boring head having an automatic balancing means. Embodiments of the present invention provide for solutions which require less parts, looser tolerances, and generally simpler geometries than known solutions. 
     As one aspect of the invention, a boring head is provided. The boring head comprises: a housing disposed about a central longitudinal axis, the housing having a first end adapted to be coupled to a machine tool and an opposite second end, the opposite second end having a moveable portion structured to have a cutting insert selectively coupled thereto; and a movement transmission mechanism disposed at least one of on or in the housing. The movement transmission mechanism comprises: a rotatable member mounted to be rotatable relative to the housing; a balancing mass having a pair of opposing grooves defined in an outer surface thereof and each cooperatively engaged by a respective alignment pin extending inward from the housing; and a primary member disposed in the housing, the primary member being moveable along the longitudinal axis and operationally coupled to the rotatable member, the balancing mass, and the moveable portion. Rotation of the rotatable member a predetermined amount causes movement of the moveable portion a corresponding first predetermined distance in a first radial direction with respect to the longitudinal axis and movement of the balancing mass a corresponding second predetermined distance in a second radial direction opposite the first radial direction. 
     Each of the opposing grooves may be disposed at an angle with respect to the central longitudinal axis. 
     The primary member may be operatively coupled to the rotatable member via a drive key which engages the rotatable member. 
     The rotatable member may comprise a ring including an inner surface having a threaded portion that cooperatively engages a threaded portion on the drive key. 
     The rotatable member may comprises a ring including an inner surface having a threaded portion that cooperatively engages a first threaded portion disposed at a first end of the drive key and a second threaded portion disposed at an opposite second end of the drive key. 
     Rotation of the rotatable member a predetermined amount may cause movement of the moveable portion a corresponding first predetermined distance in a first radial direction with respect to the longitudinal axis and movement of the balancing mass a corresponding second predetermined distance in a second radial direction opposite the first radial direction along with movement of the balancing mass toward one of the first end or the second end of the housing. 
     The primary member may be disposed about a hollow tubular member rigidly coupled to the housing, the hollow tubular member being structured to provide for the flow of coolant from the first end to the second end of the housing. 
     The balancing mass may be constrained to movement only along an axis oriented obliquely to the central longitudinal axis. 
     Each of the opposing grooves may be disposed at an angle with respect to the central longitudinal axis and the axis oriented obliquely may be oriented at the angle with respect to the central longitudinal axis. 
     The main shaft may further comprise a linear portion and an angled portion, wherein the angled portion slidably engages an angled passage formed in a transverse rod, the transverse rod having the movable portion to which the cutting insert is structured to be coupled disposed at an end thereof. 
     As another aspect of the present invention, a boring head having a movement transmission mechanism for selectively moving a cutting insert a desired amount is provided. The movement transmission mechanism comprises: a means for selectively radially displacing the cutting insert the desired amount in a first direction; and a means for selectively radially displacing a balancing mass in a second direction opposite the first direction while also axially displacing the balancing mass. The displacement of the balancing mass in the second direction effectively counters the displacement of the cutting insert in the first direction such that rotational balance of the boring head is automatically maintained. 
     The radial displacement of the cutting insert and the radial displacement of the balancing mass may be carried out simultaneously by the movement transmission mechanism. 
     The movement transmission mechanism may be disposed in or on a housing, and the movement transmission mechanism may comprise a rotatable member adapted to be rotated a predetermined amount in order to cause the cutting insert to move the desired amount. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG. 1  shows an isometric view of a boring head in accordance with an example embodiment of the present invention; 
         FIG. 2  is an end view of the boring head of  FIG. 1 ; 
         FIG. 3  is a sectional view of the boring head of  FIG. 1  taken along line  3 - 3  of  FIG. 2 ; and 
         FIG. 4  is a sectional view of the boring head of  FIG. 1  taken along line  4 - 4  of  FIG. 2 . 
         FIG. 5  is a partial sectional view of the boring head of  FIG. 1  taken along line  3 - 3  of  FIG. 2  with a portion of the internal components shown in non-sectional form in order to show internal details of the embodiment. 
         FIG. 6  is a sectional view of the boring head of  FIG. 1  taken along line  6 - 6  of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Directional phrases used herein, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. Identical parts are provided with the same reference number in all drawings. 
     As used herein, the term “number” shall be used to refer to any non-zero quantity (i.e., one or any quantity greater than one). 
     As used herein, the term “about” shall be used to refer to a point near, or at, a particular identified point (i.e., proximate). Alternatively, the term “about” shall be used to refer that one or more elements are disposed around another element. 
     As used herein, the phrase “slidably engages” shall be used to refer to two or more elements that contact each other in a manner such that one or both of the elements may slide with respect to the other, while still maintaining contact. 
       FIGS. 1-6  depict an example boring head  10 , in accordance with a non-limiting embodiment of the present invention, for conducting precision finish-boring operations on a workpiece (not shown) when boring head  10  is rotated about a central longitudinal axis  12  by a machine tool (not shown). Referring to  FIG. 1 , boring head  10  includes a body or housing  14  of substantially cylindrical shape disposed about the central longitudinal axis  12 . The housing  14  includes a first end  16  adapted to be coupled to the previously mentioned machine tool (via any suitable means) and an opposite second end  18 . Although depicted as having a substantially cylindrical shape of generally uniform diameter, it is to be appreciated that housing  14  may be formed from a number of substantially cylindrical portions of various diameter without varying from the scope of the present invention. A cutting insert  20 , selectively coupled to a moveable portion  19  via a cartridge  22 , is provided generally at or about opposite second end  18  of housing  14 . 
     Referring to  FIGS. 1 and 3 , boring device  10  further includes a movement transmission mechanism (not numbered) which comprises a rotatable member, such as ring  24  in the illustrated embodiment, mounted to be rotatable relative to housing  14 . As described below, rotation of ring  24  a predetermined amount causes corresponding movement of the cartridge  22  in a direction perpendicular to the longitudinal axis  12  of housing  14 , thus resulting in radial displacement of cutting insert  20  in a corresponding predetermined amount. Such controlled movement is achieved through the operative or operational coupling of several components as described in detail below. In the illustrated example boring device  10 , rotatable ring  24  of the movement transmission mechanism is rotatable and externally graduated. The ring  24  is arranged to be generally coaxial with housing  14 . Although shown as a ring  24  disposed about longitudinal axis  12 , it is to be appreciated that a dial type (not pictured) rotatable member (e.g., without limitation, rotatable about an axis transverse to longitudinal axis  12 ) or other suitable member could instead be substituted for ring  24  without varying from the scope of the present invention. 
     Referring to the sectional view of  FIG. 4 , an inward facing surface (not numbered) of ring  24  is provided with a number of threads (not shown in detail) thus forming a threaded portion  28  formed generally as a female threaded portion within ring  24  with a thread pitch disposed substantially parallel to longitudinal axis  12 . Continuing to refer to the sectional view of  FIG. 4 , the threaded portion  28  of ring  24  is cooperatively engaged by correspondingly threaded portions  30  disposed at radially outward ends (not numbered) of a drive key  32 . Drive key  32  includes a central aperture  34  though which a primary member  36  is disposed, and rigidly coupled therein. As shown in the sectional views of  FIGS. 3-6 , primary member  36  is disposed coaxially with longitudinal axis  12  and, more particularly, is disposed within a central passage  38  formed in housing  14  and about a hollow tubular member  35  which is rigidly coupled to housing  14 . Such arrangement of primary member  36  within central passage  38  of housing  14  acts to constrain radial movement of primary member  36  but allows for axial movement of primary member  36  along longitudinal axis  12 . Hollow tubular member  35  provides for a passageway for the flow of coolant or other suitable fluid to pass generally from first end  16  to opposite second end  18  of housing  14 . Although shown including one drive key  32 , it is to be appreciated that multiple (i.e., 2 or more) drive keys  32  may be employed without varying from the scope of the present invention. 
     Primary member  36  is generally cylindrical in shape but may have a varying radius, such as shown in the example embodiment illustrated in the FIGS. As shown in  FIG. 3 , primary member  36  includes a linear portion  36 A and an angled portion  36 B disposed nearer second end  18  of housing  14 . Angled portion  36 B slidably engages an angled passage  64  formed in a transverse rod  66  which itself is disposed within, and slidably engages a transverse bore  68  which extends through housing  14  generally at or about second end  18 . Angled portion  36 B and angled passage  64  are preferably generally cylindrical in shape, such as shown in the illustrated embodiment, however other shapes may be used without varying from the scope of the present invention. Moveable portion  19  to which cartridge  22  and cutting insert  20  are selectively coupled, as previously described, is provided at an end of transverse rod  66  such that cutting insert  20  translates radially with respect to longitudinal axis  12  upon movement of transverse rod  66  in conjunction with axial movement of primary member  36  along longitudinal axis  12 . 
     In order to maintain static balance of the boring device  10 , a balancing mass  50  is provided within housing  14 . As shown in  FIGS. 3-6 , the balancing mass  50  is generally cylindrical in shape and includes a central bore  52  disposed about a portion  54  of primary member  36 . Central bore  52  is dimensioned with respect to such portion  54  such that balancing mass  50  is moveable radially (i.e., up and down in  FIGS. 3 and 5 , perpendicular to longitudinal axis  12 ) with respect to primary member  36 . Balancing mass  50 , however, is constrained axially with respect to primary member  36  by washers  56  or other suitable structures, such that balancing mass  50  translates along with primary member  36  within housing  14 . 
     As shown in  FIGS. 4-6 , balancing mass  50  includes a pair of external grooves  60  disposed opposite each other on the external surface  61  of the balancing mass  50  which are cooperatively slidably engaged by alignment pins  62  which extend inward from housing  12 . As shown in the partial-sectional view of  FIG. 5  in which balancing mass  50  is not shown sectioned, each groove  60  is disposed at an angle θ with respect to longitudinal axis  12  when viewed axially along pin  62  (shown in dashed line in  FIG. 5 ). Each of the alignment pins  62  slidably interact with a respective groove  60  in balancing mass  50  such that as balancing mass  50  translates axially along longitudinal axis  12  with primary member  36  (to which balancing mass  50  is axially constrained) balancing mass  50  translates in a direction transverse to the longitudinal axis  12  as dictated by groove  60 . In other words, referring to the arrangement shown in  FIG. 5 , when primary member  36  is translated to the right (i.e., toward second end  18  of housing  14 ), balancing mass  50  is translated generally downward to the right. Alternatively, when primary member  36  is translated to the left (i.e., toward first end  16  of housing  14 ), balancing mass  50  is translated upward and to the left. 
     In order to maintain static balance of boring device  10 , the particular size and required radial movement of the balancing mass  50  is dependent on the amount of unbalance (product of amount of mass displaced times displacement of such mass) caused by the radial movement of transverse rod  66  and attached components  22  and  20 . It is to be appreciated that maintaining static balance is of primary concern in a boring device  10  while the dynamic balance of such device is of lesser concern due to the relatively short length of the boring device  10  and rigidness of housing  14 . 
     In order to minimize the space occupied by the balancing mass  50 , balancing mass  50  is preferably made out of a high density material such as, for example, without limitation, tungsten alloy, although other suitable materials may be used without varying from the scope of the present invention. The balancing mass  50  is calculated to generate the same unbalance (directed in an opposite direction) as the transverse rod  66 , cartridge  22  and insert  20  (including screws). The product of the balancing mass and its displacement needs to be equal to the product of the summation of masses of  66 ,  22 ,  20  and the radial displacement thereof. It is to be appreciated that the angle θ of grooves  60  (which causes radial movement of balancing mass  50 ) does not need to be the same as the angle (not numbered) of angled portion  36 B of primary member  36 . A smaller (or less dense) balancing mass can be used if the angle θ of grooves  60  is greater (thus causing greater radial movement of balancing mass  50  per axial movement of primary member  36 ). Conversely, a larger (or more dense) mass may be required if the angle θ of grooves  60  is less steep. 
     Having thus described the basic components of the movement transmission mechanism of boring head  10 , an overview of its operation will now be provided. 
     In order to induce a desired radial movement of cutting insert  20  with respect to boring head  10 , an operator simply rotates ring  24  a desired amount with respect to housing  14  according to the graduations disposed on ring  24 . As ring  24  is rotated, the threaded portion  28  on the inner surface thereof interacts with the correspondingly threaded portions  30  of the drive key(s)  32 , causing the drive key(s)  32 , along with the primary member  36  rigidly coupled thereto, to translate along the axis  12  either toward first end  16  or toward second end  18  of housing  14 , depending on the direction in which ring  24  is rotated (as well as the handedness of the correspondingly threaded portions  28  and  30 ). 
     When the primary member  36  is thus caused to translate axially along the longitudinal axis  12 . As previously discussed, as primary member  36  translates toward second end  18  of housing  14 , the interaction between angled grooves  60  of balancing mass  50  and alignment pins  62  causes balancing mass  50 , in addition to being shifted axially toward second end  18 , to be shifted radially in a first direction D 1  ( FIG. 5 ) with respect to housing  14  (and thus longitudinal axis  12 ) that is downward with respect to the cross-sectional view as oriented in  FIG. 5 . In other words, such arrangement provides for the balancing mass  50  to be constrained to movement only along an axis (not shown) oriented obliquely to the central longitudinal axis  12 . 
     Concurrently with the interaction of the grooves  60  of the balancing mass  50  and the alignment pins  62  of the housing  14  as primary member  36  translates along longitudinal axis  12 , the angled portion  36 B of primary member  36  and the angled passage  64  of transverse rod  66  interact in a manner that causes transverse rod  66 , and thus cartridge  22  and cutting insert  20  which are coupled thereto, to be shifted radially in a second direction D 2  ( FIG. 5 ) with respect to housing  14  (and thus longitudinal axis  12 ) that is upward with respect to the cross-sectional view as oriented in  FIG. 5 , and notably opposite in direction to the direction D 1  ( FIG. 5 ) in which balancing mass  50  is simultaneously moved. 
     Alternatively through such interactions, translation of primary member  36  toward first end  16  of housing  14  (as caused by rotation of ring  24  in the opposite direction from the previous example) results in balancing mass  50  being translated in a direction opposite D 1  (as well as toward first end  16 ) while cutting insert  20  is translated inward (opposite D 2 ) toward longitudinal axis  12 . 
     It is to be appreciated that through such arrangement of the movement transmission mechanism, any change to the overall balance of the boring tool  10  resulting from radial movement of the cutting insert  20  and related components is automatically compensated by the movement of the balancing mass  50  in the opposite direction. 
     From the foregoing it is to be appreciated that embodiments of the present invention provide superior balancing solutions as compared to those presently available for boring tools. Among such improvements is a reduced number of complex parts, reduced complications resulting from misalignment of parts, and reduced manufacturing costs due to both reduced complexity of parts as well as reduction in the overall number of parts needed. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to the details provided herein could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof. 
     In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” or “including” does not exclude the presence of elements or steps other than those listed in a claim. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. In any device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain elements are recited in mutually different dependent claims does not indicate that these elements cannot be used in combination.