Abstract:
Briefly, according to this invention, there is provided a balancing assembly for balancing a rotating member and the combination of a rotating member and balancing assembly. The balancing assembly includes an annular ring, a locking member and a cover. The annular ring has an opening for receiving the rotating member and at least one removable primary balancing weight and at least one removable secondary balancing weight. The locking member secures the annular ring with respect to the rotating member. The cover operatively contains the secondary balancing weight with respect to the annular ring and includes a connecting section for removably coupling the cover to the annular ring.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a balancing assembly for a rotating member. More particularly, this invention relates to a balancing assembly for balancing a rotating member such as a tool holder. 
     2. Description of the Related Art 
     The balancing of rotating members that rotate at high rates, e.g., 10,000 rpm or higher is very important. If a high speed rotating member is allowed to operate in an unbalanced state this will result in oscillating forces being created by the rotating member due to the centrifugal force effect of the unbalance. In cutting tools, this typically leads to premature bearing wear or failure and machine vibrations which result in uneven cutting action. 
     To minimize the unbalanced effects on the rotating member, for example the tool holder, the assembly must be accurately balanced. The problem of accurately balancing a rotating member is particularly acute when there is a significant change in the shape or size of the rotating member over time. For example, the tool holder must be rebalanced each time there is a change in tools or when reshaping the same tool. It is not uncommon to find a tool itself out of balance and it is often difficult to precisely place the cutting tool where its axis is exactly aligned with the axis of the rotating tool holder. Due to the frequent need for rebalancing, there is a need for an efficient, integral, adjustable and accurate balancing assembly for such high speed rotating cutting tools. 
     The object of the present invention is to provide a balancing assembly for a rotating member. Another object of the present invention is to provide a balancing assembly for balancing a rotating member such as a tool holder. 
     SUMMARY OF THE INVENTION 
     Briefly, according to this invention, there is provided a balancing assembly for balancing a rotating member. The balancing assembly includes an annular ring, a locking member and a cover. The annular ring has an opening for receiving the rotating member and at least one removable primary balancing weight and at least one removable secondary balancing weight. The locking member secures the annular ring with respect to the rotating member. The cover operatively contains the secondary balancing weight with respect to the annular ring and includes a connecting section for removably coupling the cover to the annular ring. 
     The combination of a balancing assembly and a rotating member is also disclosed. The rotating member may be most any suitable member that is capable of rotation such as a tool holder, axle, turbine blade, motor, and the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features of the present invention, as well as the advantages derived therefrom, will become clear from the following detailed description made with reference to the drawings in which: 
     FIG. 1 is a side view of a tool holder; 
     FIG. 2 is a cross-sectional view of the tool holder of FIG. 1 taken along line  2 — 2 ; 
     FIG. 3 is an exploded perspective view of the balancing assembly in accordance with the present invention; 
     FIG. 4 is a perspective view of a balancing assembly of FIG. 3; 
     FIG. 5 is an end view of the balancing assembly of FIG. 4; 
     FIG. 6 is a cross sectional view of the balancing assembly of FIG. 5 taken along line  6 — 6 ; 
     FIG. 7 is a perspective view of a cover of the balancing assembly of FIG. 3; 
     FIG. 8 is an end view of the cover of FIG. 7; 
     FIG. 9 is a cross sectional view of the cover of FIG. 8 taken along line  9 — 9 ; 
     FIG. 10 is a perspective view of the chuck of FIGS. 1 and 2; 
     FIG. 11 is an end view of the chuck of FIG. 10; and 
     FIG. 12 is a cross sectional view of the chuck of FIG. 11 taken along line  12 — 12 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, wherein like reference characters represent like elements, there is shown a balancing assembly  10  in accordance with the present invention for balancing a rotating member  12 . It will be appreciated that for purposes of illustrating the balancing assembly  10  of the present invention, the rotating member  12  is shown as a tool holder. The tool holder includes an outer housing  14  and a central axis  16 . A collet chuck  18  is provided as part of the outer housing  14  and includes a nose ring  20  which defines an opening within the tool holder for receiving a collet (not shown). The collet is in turn adapted to receive and hold a cutting tool, such as a drill (not shown). As shown in FIGS. 1, and  10 - 12 , the nose ring  20  comprises a generally circular ring which is detachably connectable to the tool holder. The nose ring  20  is tubularly shaped, and includes a lower end  20   a  and an upper end  20   b  having screw threads  20   c  on its inner diameter that engage screw threads present on the outer diameter of the distal end of the tool holder. To facilitate the grip of an operator around the nose ring  20 , a plurality of spanner slots or wrench grip recesses  20   d  are provided in the positions shown. 
     The balancing assembly  10  of the present invention may be used with equal facility to balance most any suitable member that is capable of rotation such as an axle, turbine blade, motor, and the like and the description of the invention with respect to a tool holder is not to be construed as limitation of the invention except as otherwise claimed. 
     Referring to the figures, the balancing assembly  10  is illustrated as being rotatively journalled on the rotating member  12  to balance the rotating member. The balancing assembly  10  includes an annular ring  22 , a cover  24 , at least one removable primary balancing weight  26  and at least one removable secondary balancing weight  28 . 
     The annular ring  22  is of a single unitary construction having a forward face  30  and a rearward face  32 . An opening  34  is provided within the annular ring  22  to define an inner circumferential surface  36  and an outer circumferential surface  38 . The inner circumferential surface  36  has a central axis  40  coaxial with the central axis  16  of the rotating member  12  positioned therein. Formed within the annular ring  22  are a plurality of apertures  42  into which primary balancing weights  26  are secured in a spaced relationship around the opening  34  to provide an unbalanced annular ring of symmetrical size and shape. 
     It will be appreciated that the inner circumferential surface  36  of the annular ring  22  may be profiled to conform to the shape of the rotating member  12  positioned therein. For example, the inner circumferential surface  36  of the annular ring  22  may have a truncated conical shape whose diameter gradually decreases from the forward face  30  to the rearward face  32  of the annular ring in a direction of the thickness of the ring. 
     The apertures  42  of the annular ring  22  are formed, in the example shown, in the forward face  30  of the annular ring and comprise six circumferentially spaced apertures. A primary balancing weight  26  is removably disposed within one or more of the apertures  42  in accordance with the direction of imbalance to be eliminated. In a preferred embodiment, the apertures  42  are threaded and the primary balancing weights  26  are similarly threaded to be screwed and securely retained within the apertures. 
     To maintain the annular ring  22  fixed with respect to the rotating member  12 , the annular ring includes a locking member  44 . In a preferred embodiment, the locking member  44  is formed transversely of the opening  34  and all the way through the body of the annular ring. In a preferred embodiment, as shown in FIG. 3, the locking member  44  comprises a set screw  46  that is adapted to thread within a threaded bore  48  within the annular ring  22  to secure the annular ring from rotational movement and maintain the annular ring in a fixed position with respect to the rotating member when tightened against the rotating member. The set screw  46  may be located above a circumferential groove  50  formed within the rotating member  12  as a means for positioning and controlling the axial location of the annular ring  22  with respect to the rotating member. When the set screw  46  is fully threaded within the threaded bore  48  an end of the set screw is located within the groove  50  of the rotating member. 
     Formed radially about the circumference of the rearward face  32  of the annular ring  22  are a plurality of slots  52 . In a preferred embodiment, the slots  52  have an open end  52   a  and open side  52   b  for easy access and are equally spaced about the entire circumference of the annular ring  22 . The slots  52  extend longitudinally from the rearward face  32  of the annular ring and parallel to the central axis  40  of the annular ring. Alternatively, the slots  52  may extend in directions having angles with respect to the central axis  40 , for example, in directions with which they come outwardly or inwardly in radial directions toward the central axis. The slots  52  are configured to accept at least one secondary balancing weight  28 . The secondary balancing weight  28  is of a weight different from the primary balancing weight  26  and preferably less than the primary balancing weight. The removable secondary balancing weight  28  may be of most any suitable size and shape to fit within the slot  52 . In a preferred embodiment, the secondary balancing weight  28  is capable of being apportioned incrementally into any desired weight. For example, the secondary balancing weight  28  may be of a hardening or nonhardening material having a consistency similar to clay that readily adheres to the slot surface  52 . For example, the secondary balancing weight may be mixture of powdered metal and clay or some other substance having a consistency similar to clay. The secondary balancing weight  28  may be apportioned into most any desired amount and added or subtracted to one or more of the slots  52  as desired. It will be appreciated that the secondary balancing weight  28  facilitates fine adjustment of the balancing assembly  10  beyond that obtained by the primary balancing weight  26  alone. 
     As shown in FIGS. 3, and  7 - 9 , the cover  24  of the balancing assembly  10  is configured to fit over the rearward face  32  of the annular ring  22  and enclose the slots  52  to retain the secondary balancing weights  28  within the slots during rotation of the annular ring. 
     As shown in FIGS. 7-9, the cover  24  includes a main body member  54  and a radially inwardly projecting flange  56 . Extending forwardly from the main body member  54  is a connecting section  58 . In a preferred embodiment, the connecting section  58  includes self-aligning finger-like projections  60  having opposing outwardly directed tabs  62  which are received within suitably configured openings  64  formed within the annular ring  22  to removably couple the cover  24  to the annular ring. During high-speed rotation, the balancing assembly  10  will undergo centrifugal loading and the finger-like projections  60  will tend to move radially outwardly thereby maintaining a secure hold on the annular ring  22  without the use of separate mechanical fasteners such as screws, bolts and the like. It will be appreciated that the application of separate mechanical fasteners to couple the cover  24  to the annular ring  22  after the rotating member  12  has been set to a zero net balance state will negatively effect the desired balance of the balancing assembly  10 . 
     The annular ring  22  and cover  24  can be assembled to the rotating member  12 , for example, by positioning the annular ring and cover, in this order, onto the rotating member, screwing one or more primary balancing weights  26  within one or more apertures  42  and then locking the annular ring to the rotating member. The rotating member  12  is then rotated and the direction of imbalance and the imbalance amount are measured. Then, the set screw  46  is loosened to such a degree that the annular ring  22  is rotated relative to the rotating member  12 . The annular ring  22  may be provided with an indexing mark on its outer edge. In a preferred embodiment, the center of gravity of the annular ring  22  lies on the radial axis of the set screw threaded bore  48  which serves as an indexing mark. The indexing mark is used to position the balancing assembly  10  with respect to the rotating member  12 . The annular ring  22  is rotated relative to the measured direction of imbalance to offset the imbalance of the rotating member  12 . 
     Thereafter, the rotating member  12  is rotated and the direction of imbalance and the imbalance amount are measured again. It will be appreciated that there are commercially available machines for determining the imbalance of a rotating member  12  such as a tool holder and cutting tool such as a MT-50 Tool Holder Balancer manufactured by American Hofinann. In determining the imbalance associated with the rotating member  12 , there will be both a magnitude imbalance determined and also the angular position of that magnitude imbalance will be determined. Next, one or more secondary balancing weights  28  may be added to the slots  52  to fine tune the balance of the rotating member  12 . Finally, the cover  24  is coupled to the annular ring  22  to maintain the secondary balancing weights  28  in position. 
     It will be appreciated that the annular ring  22  and the cover  24  may also be coupled loosely with each other in advance and secured to the rotating member  12  as described above. In a condition where the annular ring  22  and the cover  24  are assembled to the rotating member  12  as described above, there is no possibility that the annular ring and cover may move relative to each other, and accordingly, loosening of the balancing assembly  10  is prevented. 
     The balancing assembly  10  of the present invention can be incorporated into any rotating member  12  including a rotating cutting tool holder as shown in the figures or can be retrofitted into an existing rotating cutting tool holder. In this regard, many cutting tool manufacturers design rotating cutting tools such that the size of certain portions of the tool assembly conform to or fall within an industry standard tool envelope such as set by ANSI or ISO. Typically, the area of concern (i.e. the area to which the standard applies) is that area of the tool holder, as viewed in FIG. 1, extending forwardly from the balancing assembly. This enables conforming tool assemblies to be interchangeable. 
     The documents, patents and patent applications referred to herein are hereby incorporated by reference. 
     While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.