Abstract:
Apparatus and methods for coupling a driving shaft and a mating tool shaft to transmit rotational forces and axial tension and compression forces between the shafts. The coupler provides for axial tension transmission through tension transmission surfaces spaced-apart from torque and compression transmission surfaces of the mating tool shaft. Reversible shaft locking means prevent accidental disconnection of the driving shaft and mating tool shaft. A separate safety lock release attachment is preferably removed during tool shaft rotation and can automatically hold the driving shaft stopped when used to release the shaft locking means for a tool change. An optional reversible mechanical interlock further ensures that the driving shaft will remain stopped during a tool change. Malfunciton (e.g., improper seating) of the shaft locking means with the attachment ring in place results in a positive visual indication of the malfunction.

Description:
This application is a continuation of U.S. application Ser. No. 09/068,370, filed May 7, 1998, now U.S. Pat. No. 6,062,575, which was the national stage of International Application No. PCT/US95/15723 filed Dec. 1, 1995, which is a continuation-in-part of U.S. application Ser. No. 08/281,489, filed Jul. 27, 1994, now U.S. Pat. No. 5,490,683. 
    
    
     BACKGROUND 
     FIELD OF THE INVENTION 
     The invention relates to methods and apparatus for reversibly coupling rotating shafts. 
     Coupling Tools to High-Speed Motors 
     Many types of rotary tools are preferably coupled to a driving shaft with a safe and reliable coupler which is also reversible (allowing for the rapid removal of a tool from the coupling and/or the coupling of one tool in place of another to a driving shaft). Applications in which there are particularly stringent safety and reliability requirements for couplers include the drilling, grinding, polishing and related material-removal operations which are inherent in many medical and dental treatment plans. Rotary tools (e.g., drills, burs, grinding wheels and cutting wheels) reversibly coupled to high-speed motors can precisely shape tooth, bone, or biocompatible implant material during certain surgical procedures. Such shaping operations often require precise tool positioning and as many as thirty tool changes in the course of a single operation. Thus, each rotating tool shaft would preferably be lockable securely into its coupler (i.e., substantially preventing its accidental disconnection from the coupler), but the lock would preferably be easily and surely reversed to allow tool insertion or removal or tool changes. 
     Surgical applications of a tool shaft coupler include a requirement to keep the total time under anesthesia as short as possible for each patient. Thus, connecting and disconnecting tools via a reversibly locking tool shaft coupler should preferably be quick and simple, even for a person wearing surgical gloves. Required motions to lock or unlock the connector, or to insert or remove a tool should be relatively uncomplicated. Further, because tools may reach rotational speeds in excess of 20,000 revolutions per minute, positive (and separate) indications would preferably be provided to clearly signify to a human operator either improper placement of a tool shaft within a coupler or inoperability of a coupler shaft lock. Moreover, once connected, a tool shaft and tool shaft coupler should not be subject to accidental unlocking (which could allow disconnection of the tool), either due to operator error or mechanical failure. Thus, a tool shaft coupler lock release mechanism would preferably comprise a separate coupler unlocking component which would be required to release the lock but which would normally be removed before the motor applies torque to the tool. Accidental failure of the operator to remove the unlocking component should not, however, pose a safety hazard during relatively brief operation of the motor. Further, accidental application of motor power to a tool shaft coupler during changing of a tool should not result in driving shaft rotation before the tool is securely locked in the coupler. 
     Tool shaft couplers should be capable of transmitting axial forces (i.e., tension or compression forces acting substantially parallel to the tool shaft longitudinal axis) alone or in combination with torque (i.e., rotational forces acting substantially about the tool shaft longitudinal axis). All such forces should be effectively transmitted, i.e., without substantial axial displacement of the tool shaft with respect to the driving shaft, without substantial rotational slippage of the driving shaft with respect to the tool shaft, and without substantial distortion of the driving shaft, tool shaft or coupler. Any tool shaft coupling failure leading to shaft displacement, deformation, distortion or slippage could lead to whipping of the tool shaft, increased vibration, tool overheating and/or tool shaft breakage. In turn, any of these events could lead to accidental uncoupling of the tool shaft from the driving shaft, leading to a risk of patient injury and possible difficulty in removing a damaged tool shaft from a coupler. These problems would be particularly acute in coupler and tool designs wherein both torque and axial forces are transmitted by substantially identical tool shaft surfaces. Hence, improved tool shaft couplers and mating tool shafts would comprise surfaces used to transmit torque which would preferably be different from those used to transmit axial forces. Even more preferably, at least some surfaces transmitting torque and axial forces would preferably be spaced apart to avoid or reduce potentially damaging stress concentrations within a tool shaft and/or driving shaft. 
     Additional sources of stress in tool and driving shafts or couplers are various vibration modes due, for example, to unbalance in couplers, tools and/or tool shafts. Vibration can also be induced by distortion of the shafts and non-concentricity of driving shafts, tool shafts and/or coupler components due to lateral and/or angular misalignment. 
     SUMMARY OF THE INVENTION 
     The invention comprises reversibly locking tool shaft couplers and mating tool shafts, and methods of using the couplers to drivingly couple a driving shaft and a mating tool shaft drivingly (effectively) engaged therewith. The couplers and mating tool shafts incorporate design improvements to enhance safety and ease of operation, and comprise surfaces and/or structures for drivingly coupling (i.e., for transmitting torque and axial forces between) a driving shaft and a mating tool shaft. Note that a driving shaft to which a tool shaft coupler of the present invention could be applied would be a driving shaft (substantially rigid or flexible) which is rotatable about a substantially longitudinal axis within a driving shaft housing. Note also that a mating tool shaft may comprise a portion of a tool itself (e.g., the shank of a drill bit or burr), or a shaft which itself is drivingly coupled with a tool shaft (e.g., a flexible or geared shaft tipped with a tool or coupled to a tool shaft). 
     A tool shaft coupler of the present invention comprises at least one torque transmission surface fixedly coupled to the driving shaft for axially slidingly mating with a mating tool shaft to transmit torque between the mating tool shaft and the driving shaft. Additionally, the coupler comprises at least one compression transmission surface as well as tension transmission means, the tension transmission means being spaced apart from the at least one compression transmission surface and the at least one torque transmission surface, and comprising at least one tension transmission surface and at least one movable tension-resisting member, the at least one tension-resisting member being reversibly and slidingly movable to a tension-resisting position to couple the driving shaft and a mating tool shaft to reversibly limit maximum axial movement of the mating tool shaft with respect to the driving shaft under an axial tension load (i.e., a force substantially parallel to the tool shaft longitudinal axis which tends to pull the driving and mating tool shafts apart). 
     The at least one compression transmission surface is fixedly coupled to the driving shaft for substantially limiting maximum axial movement of a mating tool shaft with respect to the driving shaft under an axial compression load. For reversibly locking said at least one tension-resisting member in a tension-resisting position, the invention comprises shaft locking means having an (optionally high-friction and/or mechanically engaging) engagement surface (for slidably engaging safety lock release means), the shaft locking means being slidably coupled to the driving shaft. The slidable coupling of the shaft locking means to the drive shaft may also include guide means which act to substantially prevent rotation of the shaft locking means with respect to the drive shaft while allowing substantially free sliding coupling as described herein. 
     Preferred embodiments of tool shaft couplers of the present invention may also comprise substantially toroidal safety lock release means and attachment means, the attachment means being reversibly coupled (e.g., as be screw threads or a twist-lock connector) to the driving shaft housing and serving one or more functions, as in guiding a mating tool shaft during connection to or disconnection from a coupler, supporting the tool shaft with one or more bearings, facilitating locking and/or unlocking of a coupler, and/or reducing any likelihood of tool shaft whipping (i.e., tool shaft rotation which is not substantially confined to rotation about the tool shaft longitudinal axis). The attachment means comprise at least one spindle cap access slot and may interact with the substantially toroidal safety lock release means which are slidably positionable over said attachment means and slidingly engagable through said at least one spindle cap access slot with said engagement surface of said shaft locking means to move said shaft locking means to a first unlocking position for allowing said at least one tension-resisting member to move from said tension-resisting position to allow reversible placement of a mating tool shaft within said shaft locking means, and to allow movement of said shaft locking means to a second locking position for moving said at least one tension-resisting member to said tension-resisting position and for reversibly locking said at least one tension-resisting member in said tension-resisting position. Safety lock release means may alternatively comprise (in addition to or in place of the substantially toroidal safety lock release means) a lock release lever reversibly insertable in one or more lever access ports in the attachment means and movable therein to facilitate unlocking of a coupler. 
     Besides the tool shaft coupler described herein, the present invention may additionally comprise one or more other improvements, including a mating tool shaft with correspondingly shaped and positioned axial force and torque transmission surfaces, as well as a method of coupling a driving tool shaft and a mating tool shaft, and warning means to visually indicate improper seating of a mating tool shaft in the coupler and/or malfunction of said shaft locking means. The warning means preferably comprise at least a warning portion of the attachment means and/or the mating tool shaft, each warning portion having a distinctive visual appearance and being visible to a user in case of malfunction of the shaft locking means and/or to indicate improper seating of a mating tool shaft in the coupler respectively. 
     In preferred embodiments of mating tool shafts, one or more warning bands of distinctive visual appearance may be applied to the portion of a mating tool shaft surface adjacent to and just concealed by the attachment means when the mating tool shaft is drivingly engaged with the tool shaft coupler. Because such driving (effective) engagement implies sliding insertion of the mating tool shaft within the coupler to an effective depth wherein all corresponding axial force and torque transmission surfaces on the mating tool shaft and in the coupler are substantially fully engaged, faulty engagement of the force transmission surfaces occurs when the mating tool shaft is inserted in the coupler to a depth less than the effective depth. Insertion of a mating tool shaft to a less-than-effective depth (that is, the mating tool shaft is not drivingly coupled to the tool shaft coupler) will then preferably leave visible at least part of a visually distinct proximal portion on the mating tool shaft which is unconcealed by the attachment means, thus providing a visual warning of the tool shaft&#39;s improper insertion into the coupler. This visually distinct proximal portion of the mating tool shaft would, of course, not be visible outside of the attachment means when the tool shaft is drivingly coupled to the tool shaft coupler. For embodiments comprising the toroidal safety lock release means, a visually distinctive warning portion of the attachment means would be substantially visible with the toroidal safety lock release means contacting the shaft locking means in the first (unlocking) position, and substantially invisible with the toroidal safety lock release means contacting the shaft locking means in said second (locking) position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A schematically illustrates a preferred embodiment of a tool shaft coupler including attachment means and toroidal safety lock release means in a first, unlocking, position (in partial cross-section). 
     FIG. 1B schematically illustrates a preferred embodiment of a tool shaft coupler including attachment means and toroidal safety lock release means in a second, locking, position (in partial cross-section). 
     FIG. 2 schematically illustrates the steps of a method of reversibly coupling a driving shaft and a mating tool shaft. 
     FIG. 3A schematically illustrates (in partial cross-section) a disconnected view of a driving shaft and mating tool shaft, including tension-resisting members. 
     FIG. 3B schematically illustrates (in partial cross-section) a connected view of a driving shaft and mating tool shaft, including tension-resisting members. 
     FIG. 3C schematically illustrates a cross section of a driving shaft and mating tool shaft effectively engaged as illustrated in FIG.  3 B. 
     FIG. 4 schematically illustrates (in partial cross-section) an exploded view of a tool shaft coupler, including attachment means and toroidal safety lock release means. 
     FIG. 4A schematically illustrates tool shaft coupler attachment means rotated 90 degrees relative to the attachment means view in FIG.  4 . 
     FIG. 5 schematically illustrates an exploded view of tool shaft coupler attachment means. 
    
    
     DETAILED DESCRIPTION 
     In the following description, two alternative embodiments of the mating tool shaft  50 , 50 ′ are identified, the embodiments being substantially similar except for differing forms of tension transmission surface  53 , 53 ′. Only one embodiment (i.e., either  50  or  50 ′) of a mating tool shaft is used with tool shaft coupler  15  at any one time. Since in general one or the other of the embodiments  50  and  50 ′ may be desired in certain applications, both embodiments are identified when a general reference to a mating tool shaft is required in the following discussion. Other corresponding features of mating tool shaft  50 , 50 ′ are similarly identified by unprimed and primed numbers respectively. 
     Referring to FIGS. 1A,  1 B,  3 A,  3 B,  3 C,  4 ,  4 A and  5  for schematic illustrations of the features discussed, a preferred embodiment of the invention is seen to comprise a tool shaft coupler  15  for drivingly coupling a driving shaft  60  with a mating tool shaft  50 , 50 ′ which is effectively engaged with the driving shaft  60 , the driving shaft  60  being rotatable about a substantially longitudinal axis BB within a driving shaft housing  65  (which in turn is fixedly coupled to driving shaft housing end piece  65 ′). Note that for the sake of clarity in the schematic illustrations, components and features described herein may be labeled only in the figure(s) in which they appear most clearly. 
     A mating tool shaft  50 , 50 ′ has surfaces and/or structures functionally and spatially corresponding to surfaces and/or structures within tool shaft coupler  15 . Effective engagement of a mating tool shaft  50 , 50 ′ comprises insertion of mating tool shaft  50 , 50 ′ within the tool shaft coupler  15  an effective distance which would allow substantially full mating of corresponding torque and axial force transmission surfaces and effective engagement of the mating tool shaft  50 , 50 ′ with the shaft locking means. With the corresponding torque and axial force (i.e., compression and tension) transmission surfaces, or structures comprising one or more of such surfaces of the tool shaft coupler  15  and the mating tool shaft  50 , 50 ′ thus brought into effective apposition, transmission of torque and axial compression and tension forces between the driving and mating tool shafts may then take place. However, effective engagement of a mating tool shaft  50 , 50 ′ with respect to the driving shaft  60  also facilitates reversible locking of a mating tool shaft  50 , 50 ′ within the tool shaft coupler  15 . Such locking in the present invention includes an optional safety feature wherein malfunction of which will be readily apparent to a human operator of the tool through the appearance of one or more areas of distinctive visual appearance on attachment means  17  and/or mating tool shaft  50 , 50 ′. 
     Surfaces for transmission of torque and axial forces within a tool shaft coupler  15  are preferably fixedly coupled (attached) to (e.g., as be welding, brazing, crimping, swaging, screwing, clamping, or by interference fit), or by forming as an integral part of a driving shaft  60  which, in preferred embodiments, comprises a motor shaft or a shaft which is drivingly coupled to a motor shaft (as by a flexible shaft in certain embodiments). Typically, a driving shaft  60  will be rotatable within a driving shaft housing  65 , the housing  65  (e.g., a motor stator) often providing a convenient hand grip for a human operator. Surfaces for transmission to the driving shaft  60  of (axial) tension on the mating tool shaft  50 , 50 ′ (tending to pull the mating tool shaft  50 , 50 ′ away from the tool shaft coupler  15  substantially along longitudinal axis BB) are spaced apart from the surfaces for transmission of torque and (axial) compression forces. 
     Tool shaft coupler  15  comprises at least one torque transmission surface (see, e.g., surface  64  of spindle chip  62  in FIG. 3A) fixedly coupled to the driving shaft  60  for axially slidingly mating with a corresponding torque transmission surface  54 , 54 ′ of mating tool shaft  50 , 50 ′ to transmit torque between mating tool shaft  50 , 50 ′ and the driving shaft  60 . Note that torque transmission surface  64  may, for example, be formed as an inherent part of driving shaft  60  or, as in FIGS. 1A,  1 B,  3 A,  3 B,  3 C and  4 , torque transmission surface  64  may be formed on a separate piece of material (e.g., spindle chip  62 ) which is then itself fixedly attached to driving shaft  60 . The latter configuration may be preferable in certain applications because it allows spindle chip  62  to be fabricated and hardened separately from driving shaft  60 . Note also that the configuration shown in cross section in FIG. 3C (i.e., wherein a torque transmission surface lies substantially in a single plane and has a width substantially equal to the diameter of spindle chip  62 ) may be replaced by other preferred configurations having a plurality of torque transmission surfaces lying in two or more different planes (e.g., as in a square or hexagonal drive). However, for certain relatively high-torque applications, the configuration illustrated in FIGS. 3A,  3 B and  3 C may be preferred because it provides substantial torque transmission capability with a relatively low likelihood of distortion (e.g., rounding of corners) on spindle chip  62  or mating tool shaft  50 , 50 ′. 
     Tool shaft coupler  15  also comprises tension transmission means spaced apart from said at least one torque transmission surface and comprising at least one tension transmission surface (e.g., the walls  80 , 80 ′ of substantially cylindrical holes in which balls  82 , 82 ′ respectively substantially reside as schematically illustrated) and at least one movable tension-resisting member (e.g., balls  82 , 82 ′ comprising hardened steel or, preferably, chrome alloy steel). Note that although two tension-resisting members (i.e., balls  82 , 82 ′) and two tension transmission surfaces (i.e., the walls  80 , 80 ′ of substantially cylindrical holes) are illustrated herein, one ball or more than two balls in their respective substantially cylindrical holes, spaced (preferably substantially evenly) around the circumference of driving shaft  60 , may be preferred for certain relatively high-load applications. Note further that although the illustrated embodiments of tool shaft coupler  15  comprise equal numbers of tension-resisting members and tension transmission surfaces, the number of tension-resisting members may exceed the number of tension transmission surfaces in cases where two or more tension-resisting members simultaneously engage a single tension transmission surface (e.g., two or more tension-resisting members are present substantially side-by-side in an elongated hole). 
     As illustrated, balls  82 , 82 ′ are substantially free to move substantially radially within substantially cylindrical walls  80 , 80 ′ respectively, except as limited by the inner surface  75  (the inner surface  75  itself comprising a cam surface  72 ) of spindle cap  70  (which limits movement of balls  82 , 82 ′ away from driving shaft  60 ), and by retaining ledges  85 , 85 ′ (seen best in FIG. 3A) which limit movement of balls  82 , 82 ′ respectively toward the longitudinal axis BB. Ledges  85 , 85 ′ preferably comprise substantially frusto-conically shaped surfaces which neck-down of reduce the nominal inner diameter of substantially cylindrical walls  80 , 80 ′. Ledges  85 , 85 ′ thus limit the movement of balls  82 , 82 ′ respectively toward axis BB when a mating tool shaft  50 , 50 ′ is not present within driving shaft  60  (as shown in FIG.  3 A). The portion of a mating tool shaft  50 , 50 ′ (other than any tension transmission surface) which is proximate ledges  85 , 85 ′ when the tool shaft  50 , 50 ′ is drivingly engaged in a coupler  15  is intentionally spaced apart from spindle cap  70  and other portions of the shaft locking means. Thus if balls  82 , 82 ′ that contact spindle cap  70  are not simultaneously in contact with a tension transmission surface, then they can not be in contact simultaneously with tool shaft  50 , 50 ′ in any manner. This spacing prevents balls  82 , 82 ′ (or other analogously sized tension-resisting members) from exerting purely lateral force on tool shaft  50 , 50 ′ during normal operations, and thus tends to reduce tool shaft vibration in cases where tool shaft  50 , 50 ′ is not exactly coaxial with driving shaft  60 . In combination with the lateral clearance provided between tool shaft  50 , 50 ′ and driving shaft  60 , the function of tension-resisting members in the present invention approximates a (laterally and longitudinally) complaint universal joint for tool shaft  50 , 50 ′ which allows the shaft to “float” to a limited extent while still restrained, the (lateral and/or longitudinal) floating action acting to reduce transmission of vibration from the tool shaft  50 , 50 ′ to the driving shaft  60  (and thence to the hand of the operator in certain preferred embodiments). 
     Tool shaft  50 , 50 ′ is preferably substantially oriented with respect to driving shaft  60  by one or more bearings (distal and proximal journal bearings  22 , 22 ′ respectively are schematically illustrated in FIG. 5) within attachment means  17 . Substantially coaxial tool shaft orientation as above by one or more bearings  22 , 22 ′ of attachment means  17  may include errors due to lateral displacement and/or angular displacement with respect to driving shaft  60 . The above spaceing conditions regarding tension-resisting members are beneficial in reducing adverse effects (e.g., vibration and wear) due to possible orientation error(s). 
     But for effective retention when a mating tool shaft  50 , 50 ′ is inserted within driving shaft  60  so as to effectively engage torque transmission surface  64  (as shown in FIGS.  1 B and  3 B), ledges  85 , 85 ′ do allow balls  82 , 82 ′ respectively to move into a tension-resisting position, which would allow substantially simultaneous (interference) contact of balls  82 , 82 ′ with both substantially cylindrical walls  80 , 80 ′ respectively and tension transmission surface  53 , 53 ′ of mating tool shaft  50 , 50 ′. If the balls  82 , 82 ′ are held in such a tension-resisting position (e.g., by the inner surface  75  of spindle cap  70 , as shown in FIG.  1 B), mating tool shaft  50 , 50 ′ could not be disconnected (i.e., withdrawn) from effective engagement with torque transmission surface  64  by a tension force tending to separate driving shaft  60  and mating tool shaft  50 , 50 ′ which is applied substantially parallel to longitudinal axis BB. Such a tension force would put balls  82 , 82 ′ in compression because of the interference nature of such a tension-resisting position. Note that the groove  52 , 52 ′, one portion of which is tension transmission surface  53 , 53 ′, is preferably deep enough so that balls  82 , 82 ′ never touch the groove surface closest to axis BB (i.e., balls  82 , 82 ′ preferably can not bottom out in groove  52 , 52 ′). 
     Note also that balls  82 , 82 ′ are shown in similar tension-resisting positions in FIG.  1 B and in FIG. 3B, but with mating tool shafts  50  and  50 ′ in the two figures respectively. The difference between mating tool shafts  50  and  50 ′, which is schematically illustrated in FIGS. 1B and 3B respectively, is that mating tool shaft  50  comprises groove  52  and tension transmission surface  53  (see FIG.  4 ), whereas mating tool shaft  50 ′ comprises groove  52 ′ and tension transmission surface  53 ′. Surface  53 , as illustrated in FIG. 4, lies substantially entirely in a plane which is itself substantially perpendicular to longitudinal axis BB. Thus, contact of balls  82 , 82 ′ with surface  53  is substantially limited to its outer (substantially circular) peripheral edge. 
     In contrast, tension transmission surface  53 ′ is a substantially frusto-conically shaped surface which is substantially symmetrical about longitudinal axis BB, surface  53 ′ being oriented to allow balls  82 , 82 ′, when in tension-resisting positions, to contact portions of surface  53 ′ which are closer to longitudinal axis BB than the outer (substantially circular) periphery of the surface  53 ′. Tension transmission by surface interference contact between balls  82 , 82 ′ and surface  53 ′ may better limit axial free play between driving and mating tool shafts (compared to interference contact between balls  82 , 82 ′ and the outer edge of surface  53 ) in certain applications having relatively high axial tension loads tending to separate a tool shaft from tool shaft coupler  15 . Assuming a substantially fixed distance between an interference tension-resisting position of a tension-resisting member (e.g., one of the balls  82 , 82 ′) and the compression transmission surface  67  (see FIG. 3A) of a tool shaft coupler  15 , axial free play then becomes substantially a function of the distance between compression transmission surface  67  and tension transmission surface  53  or  53 ′ on a mating tool shaft  50  or  50 ′ respectively (the latter measurement is labeled X′ on FIG.  3 A). In certain applications, surface  53 ′ is more protected (and thus less subject to wear) than the peripheral edge of surface  53 . Edge wear on surface  53 , when combined with normal manufacturing tolerances, may then result in unacceptably large values of possible relative motion (free play) between driving shaft  60  and mating tool shaft  50 , substantially along longitudinal axis BB, even when balls  82 , 82 ′ are very repeatably moved into tension-resisting positions. 
     The said at least one tension-resisting member (e.g., balls  82 , 82 ′ for illustrative purposes) is reversibly and slidingly movable through the action of the inner spindle cap surface  75 , which in turn comprises a cam surface  72 . Spindle cap  70  is springingly coupled to driving shaft  60  through the action of spring  78  acting on spring stop ring  79 . Spring stop ring  79  in turn rests against driving shaft shoulder  61  to transfer the force of spring  78  to driving shaft  60 . Spindle cap  70  is retained on driving shaft  60  by spindle cap nut  74 . 
     Thus, if spindle cap  70  is first moved to compress spring  78  (i.e., moved toward the right as in FIG. 1A to a first or unlocking position), a mating tool shaft  50 , 50 ′ may, if present within coupler  15 , be substantially freely withdrawn from coupler  15 . If, on the other hand, a mating tool shaft  50 , 50 ′ is not effectively engaged in coupler  15  when spindle cap  70  is moved to a first (unlocking) position, a mating tool shaft  50 , 50 ′ may then be inserted and effectively engaged with torque transmission surface  64 . Spindle cap  70  may then be released to move to the left toward its resting position with spring  78  extending and cam surface  72  contacting balls  82 , 82 ′ (as in FIG.  1 B). As cam surface  72  contacts both balls  82 , 82 ′, the balls are substantially simultaneously moved by cam surface  72  into tension-resisting positions (assuming a mating tool shaft  50  or  50 ′ is at that time inserted sufficiently far into coupler  15  to effectively engage with torque transmission surface  64 ). When cam surface  72  has maximally moved balls  82 , 82 ′ into tension-resisting positions, continued movement of spindle cap  70  in a direction which would tend to extend spring  78  is effectively stopped by spindle cap nut  74 . The interference tension-resisting positions of balls  82 , 82 ′ thus act to couple the driving shaft  60  and a mating tool shaft  50  (or  50 ′) to reversibly limit (in conjunction with compression transmission surfaces  55  or  55 ′ and  67 ) maximum axial movement (i.e., movement substantially parallel to longitudinal axis BB) of the mating tool shaft  50 , 50 ′ with respect to the driving shaft  60  under alternating axial compression and tension loads. Such maximum axial movement is preferably less than about 0.020 inches to improve mating tool shaft placement precision, more preferably less than about 0.010 inches to reduce the risk of shaft vibration and most preferably less than about 0.005 inches to reduce wear on components of tool shaft coupler  15 . Note that alternate compression transmission surfaces  57  or  57 ′ and  67 ′ may act in an analogous manner to that described above for compression transmission surfaces  55  or  55 ′ and  67  to reversibly limit maximum axial movement of a mating tool shaft  50 , 50 ′. When so acting, compression transmission surface  57  or  57 ′ is preferably spaced apart from the corresponding tension transmission surface ( 53  or  53 ′ respectively) by a distance (indicated by X″ in FIG. 3A) which will limit maximum axial tool shaft movement in the manner described above. 
     All embodiments of tool shaft couplers  15  of the present invention comprise at least one compression transmission surface (see, e.g.,  67  in FIG. 3A) fixedly attached to the driving shaft  60  for substantially limiting, in conjunction with at least one corresponding compression transmission surface on a mating tool shaft  50 , 50 ′, maximum axial movement of a mating tool shaft  50 , 50 ′ with respect to the driving shaft  60  under an axial compression load. Compression transmission surface  67  in the illustrated embodiment of tool shaft coupler  15  has substantially the same shape and cross-sectional area as that portion of mating tool shaft  50 , 50 ′ (i.e., compression transmission surface  55 , 55 ′ respectively) illustrated in cross-section in FIG. 3C (i.e., substantially a semicircle having substantially one-half of the cross-sectional area of mating tool shaft  50 , 50 ′ as illustrated). Note that compression transmission surface  67  may be reduced in size (e.g., by chamfering its edges) if the resulting area would substantially match or mate with the corresponding mating tool shaft compression transmission surface  55 , 55 ′, and if the size reduction would not result in excessive material stress (i.e., leading to permanent deformation or premature failure) under the anticipated axial compression load. 
     The invention also comprises shaft locking means having an engagement surface  71  and being slidably coupled to the driving shaft  60  for reversibly locking said at least one tension-resisting member (i.e., balls  82 , 82 ′) in a tension-resisting position. The shaft locking means in the illustrated embodiments comprises the spring stop ring  79 , spring  78 , spindle cap  70 , and spindle cap nut  74 , some interactions of which are described above. Note that the outer surface  73  of spindle cap  70  comprises a substantially frusto-conical surface  71  which in the illustrated embodiments functions as the engagement surface of the shaft locking means. Functions of the engagement surface  71  are described below. 
     In preferred embodiments, shaft locking means of the present invention may also comprise guide means for the shaft locking means. The guide means, in turn, may comprise one or more substantially longitudinal splines  87  on the stop ring  79  (which is then fixedly attached to driving shaft  60 ) matable with correspondingly spaced and numbered substantially longitudinal grooves  88  on the proximate surface of the shaft locking means (that is, on inner spindle cap surface  75  as schematically illustrated in FIGS.  1 A and  1 B). Alternative embodiments of the guide means (as in FIG. 4) may comprise one or more pairs of correspondingly spaced grooves or depressions  66 , 76  on proximate surfaces of the driving shaft  60  and/or spring stop ring  79  and the spindle cap  70  respectively, each pair of corresponding grooves or depressions  66 , 76  being coupled via one or more ball bearings  77  substantially free to roll and/or slide within the corresponding grooves or depressions  66 , 76  (but not outside of the grooves or depressions  66 , 76 ) when the shaft locking means is slidingly moved longitudinally with respect to the driving shaft  60 . In either the spline/groove embodiment or the ball bearing/groove or depression embodiment, the shaft locking means will be substantially prevented by the guide means from rotating with respect to the driving shaft  60  about the rotational axis of the driving shaft (i.e., longitudinal axis BB), its preferred motion instead being a sliding motion in directions substantially parallel to the longitudinal axis BB. 
     Preferred embodiments of the invention may additionally comprise safety lock release means and attachment means  17 . Attachment means  17  comprises at least one spindle cap access slot  32  (illustrated in two views in FIGS.  4  and  4 A). Attachment means  17  may be reversibly coupled to the driving shaft housing end piece  65 ′ (e.g., as by screw threads (as illustrated in FIGS.  1 A and  1 B), or a twist-lock connector which tends to be tightened when attachment means  17  is rotated in the expected direction of rotation of mating tool shaft  50 , 50 ′) for guiding and supporting the mating tool shaft  50 , 50 ′. 
     Various sizes of attachment means  17  are illustrated in FIGS. 1A,  1 B,  4 ,  4 A and  5 , each comprising a tubular attachment shaft  20 , the proximal end of which may be reversibly secured within (e.g., as by set screw  35 ) or fixedly attached to attachment base  30 . Within attachment shaft  20  are firmly but removably mounted at least one distal journal bearing  22  and at least one spacer tube  23 . Note that journal bearing  22  (and, similarly, journal bearing  22 ′), as well as any other journal bearings of the present invention, each comprise one or more bearing elements, such as a ball bearing, a roller bearing or a sleeve bearing or some combination of such bearing elements. When a journal bearing comprises more than one bearing element, the adjacent bearing elements are preferably spaced apart distances less than or equal to the length of a single bearing element. 
     The journal bearing  22  is closely and slidably matable with a mating tool shaft  50 , 50 ′, and the distal end of mating tool shaft  50 , 50 ′ extends beyond the distal bearing  22  a second spacing distance when the tool shaft is drivingly coupled. The spacer tube acts to maintain a desired bearing mounting position as described below. 
     In the embodiment illustrated in FIG. 5, attachment means  17  comprises attachment shaft  20 , two bearings  22 , 22 ′ and two spacer tubes  23 , 23 ′, both bearings  22 , 22 ′ and both spacer tubes  23 , 23 ′ being mounted substantially symmetrically about longitudinal axis BB within attachment shaft  20 . Note that when attachment means  17  is coupled to driving shaft housing  65  (through driving shaft housing end piece  65 ′) as in FIGS. 1A and 1B, a mating tool shaft  50 , 50 ′ which is reversibly coupled to driving shaft  60  via coupler  15  will tend to be rotatable substantially about longitudinal axis BB. Any whipping tendency of mating tool shaft  50 , 50 ′ will be at least substantially reduced by the guiding action of bearings  22 , 22 ′ through which mating tool shaft  50 , 50 ′ passes. 
     As noted above, certain embodiments of the tool shaft coupler  15  may have only one distal being  22  near the distal end of attachment shaft  20  (as when bearing  22 ′ and its associated spacer tube  23 ′ are not present). On the other hand, in embodiments of the tool shaft coupler  15  which comprise both bearings  22  and  22 ′ and their associated spacer tubes  23  and  23 ′ (as schematically illustrated in FIG.  5 ), then spacer tubes  23 , 23 ′ and bearing  22 ′ establish a first spacing distance between distal bearing  22  and the tension-resisting member(s) (e.g., balls  82 , 82 ′). Spacer tube  23  establishes a bearing-spacing distance between distal journal bearing  22  and proximal journal bearing  22 ′. When a mating tool shaft  50 , 50 ′ is drivingly coupled to coupler  15 , the distal end of tool shaft  50 , 50 ′ extends distally to distal bearing  22  a second spacing distance. 
     In embodiments of tool shaft coupler  15  comprising proximal and distal bearings spaced as above, it has been empirically determined that vibration associated with high-speed rotation of a mating tool shaft  50 , 50 ′ is minimized when the first spacing distance is greater than the second spacing distance and particularly when the second spacing distance approximately equals the bearing-spacing distance. 
     Substantially toroidal safety lock release means  18  are slidably positionable over said attachment means  17  and slidingly engagable through said at least one spindle cap access slot (e.g., access slots  32 , 32 ′) with said engagement surface (e.g., see  71  on FIGS. 1A,  1 B and  4 ) of said shaft locking means to move said shaft locking means to a first (unlocking) position (e.g., see the position of spindle cap  70  in FIG. 1A) for allowing said at least one tension-resisting member (e.g., see balls  82 , 82 ′) to move from said tension-resisting position to allow reversible placement of a mating tool shaft  50 , 50 ′ within said shaft locking means, and to allow movement of said shaft locking means to a second (locking) position (e.g., see the position of spindle cap  70  in FIG. 1B) for moving said at least one tension-resisting member (balls  82 , 82 ′) to said tension-resisting position and for reversibly locking said at least one tension-resisting member (balls  82 , 82 ′) in said tension-resisting position. 
     Toroidal safety lock release means  18  comprise at least one radially directed pin  42  (two substantially diametrically opposed pins  42 , 42 ′ are illustrated in FIGS. 1A,  1 B and  4 ) mounted fixedly in attachment ring  40  and extending far enough toward ring  40 &#39;s longitudinal axis (e.g., see axis BB in FIGS. 1A,  1 B and  4 ) to contact engagement surface  71  of spindle cap  70  through slot  32  in attachment means  17  (slots  32 , 32 ′ are illustrated in FIGS. 1A,  1 B and  4  to accept the two pins  42 , 42 ′ which are also illustrated). Note that, because its larger diameter provides a convenient finger-gripping surface, toroidal safety lock release means  18  can be used to facilitate manually tightening or loosening attachment base  30  from its coupling (illustrated in FIGS. 1A and 1B as threaded) to driving shaft housing end piece  65 ′. 
     The tool shaft coupler shaft locking means engagement surface  71  may also interact with the safety lock release means to result in a driving shaft break-away torque of at least one inch-ounce with the safety lock release means in the first, unlocking, position. Note that engagement surface  71  and pins  42 , 42 ′ may optionally be given complementarily formed or otherwise relatively high-friction surface finishes (e.g., as with matching machined grooves, knurling, sand-blasting or coating with frictional material). Sufficient friction force may then be developed between the pins  42 , 42 ′ and engagement surface  71  to assure that sufficient braking force acts on spindle cap  70  (and thence through guide means to driving shaft  60 ) to exceed the break-away torque applied to driving shaft  60 . This condition reversibly prevents rotation of driving shaft  60  with respect to driving shaft housing  65  when manual pressure is applied to attachment ring  40  to move (through pressure exerted by pins  42 , 42 ′ on engagement surface  71 ) spindle cap  70  substantially into a first, unlocking position. Note that for substantial (but still reversible) prevention of driving shaft  60  rotation with respect to driving shaft housing  65 , complementary pin engagement means may optionally be employed. Complementary pin engagement means comprise at least one pin pair  91 , 92  fixedly coupled in opposing surfaces of spindle cap  70  and driving shaft housing end piece  65 ′ as schematically illustrated in FIGS. 1A and 1B. Each pin pair  91 , 92  is sized and located so that the pins will overlap (see FIG. 1A) and thus mechanically (and reversibly) substantially prevent rotation of driving shaft  60  with respect to driving shaft housing end piece  65 ′ (and thus with respect to driving shaft housing  65 ) when spindle cap  70  is in a first (unlocking) position. On the other hand, pin pair  91 , 92  is also sized so that the pins will not overlap (see FIG. 1B) and thus will not prevent rotation of driving shaft  60  with respect to driving shaft housing end piece  65 ′ (and thus with respect to driving shaft housing  65 ) when spindle cap  70  is in a second (locking) position. For balance, preferred embodiments of the present invention which incorporate at least one pin pair  91 , 92  will preferably incorporate a plurality of such pin pairs spaced substantially equally around opposing surfaces of spindle cap  70  and driving shaft housing end piece  65 ′. When present, each pin pair  91 , 92  will preferably comprise ramp-like surfaces and be so spaced as to substantially prevent end-to-end interference between pins of a pin pair  91 , 92  when spindle cap  70  is being moved from a second (locking) position to a first (unlocking) position. In these latter embodiments, pin pairs  91 , 92  will still substantially (and reversibly) prevent rotation of driving shaft  60  with respect to driving shaft housing end piece  65 ′ (and thus with respect to driving shaft housing  65 ) when spindle cap  70  is in a first (unlocking) position, but the pin pair(s)  91 , 92  will not substantially impede movement of spindle cap  70  into the first (unlocking) position. 
     Note also that attachment means  17  may additionally comprise in preferred embodiments warning means to visually indicate malfunction of said shaft locking means. Malfunction of the shaft locking means embodiments illustrated herein would result from a failure of spindle cap  70  to move from a first (unlocking) position to a second (locking) position under the influence of spring  78 . Such failure to move even when no restraint is imposed through attachment ring  40  may be caused by a broken spring  78  and/or improper insertion of a mating tool shaft  50 , 50 ′ through the tension transmission means resulting in a failure to effectively engage the mating tool shaft  50 , 50 ′ with torque transmission surface  64 . Failure to effectively engage torque transmission surface  64  will cause tension transmission surface  53 , 53 ′ of the mating tool shaft  50 , 50 ′ respectively to be positioned too far from a movable tension-resisting member (e.g., balls  82 , 82 ′) to engage such member as attempts are made to move the member into an interference tension-resisting position. This is the condition illustrated schematically in FIG.  1 A. Hence, with driving shaft  60  and mating tool shaft  50  in the relative positions illustrated in FIG. 1A, substantial release of manual pressure on attachment ring  40  will not result in spindle cap  70  moving to a second, locking, position where warning surface  99  would be substantially invisible (the condition illustrated in FIG.  1 B). On the contrary, substantial release of manual pressure on attachment ring  40  under this condition will cause attachment ring  40  to remain in a position where warning surface  99  would remain substantially visible. Similar results would obtain in the case where attachment ring  40  was used to withdraw spindle cap  70  into a first, unlocking, position either after or simultaneous with breakage of spring  78 . 
     Thus, warning means in preferred embodiments comprise at least a warning surface portion of said attachment means having a distinctive visual appearance (see, e.g., warning line  99  in FIGS. 4,  4 A and  5 ), said warning portion being substantially visible with said toroidal safety lock release means contacting the shaft locking means in said first (unlocking) position, and said warning portion being substantially invisible with said toroidal safety lock release means contacting the shaft locking means in said second (locking) position. The desired distinctive visual appearance of the warning portion of the attachment means may be achieved, for example, with a contrasting surface finish or texture (e.g., knurled, matte or polished or machined grooves) and/or color (e.g., a yellow stripe on black) relative to adjacent attachment means surfaces. 
     The invention also comprises a mating tool shaft (e.g.,  50 , 50 ′) for coupling with a driving shaft  60  via a tool shaft coupler  15  as described herein, the mating tool shaft comprising at least one torque transmission surface  54 , 54 ′, at least one tension transmission surface  53 , 5340  , and at least one compression transmission surface  55 , 55 ′. The torque transmission surface (e.g.,  54 ′ in FIG. 3A) is fixed coupled to (or an integral part of) the mating tool shaft (e.g.,  50 ′ in FIG. 3A) for axially slidingly mating with said at least one torque transmission surface (e.g.,  64  in FIG. 3A) of the tool shaft coupler  15  to transmit torque between the mating tool shaft  50 , 50 ′ and the driving shaft  60 . 
     At least one tension transmission surface (e.g.,  53 ′ in FIG. 3A) is spaced apart from said at least one torque transmission surface (e.g.,  54  in FIG. 3A) to couple reversibly with said at least one movable tension-resisting member (e.g., balls  82 , 82 ′) of the tool shaft coupler  15  to couple the driving shaft  60  and the mating tool shaft (e.g.,  50 ′ in FIG.  3 A). Such coupling reversibly limits, in conjunction with at least one compression transmission surface fixedly coupled to (or an integral part of) the mating tool shaft and at least one compression transmission surface of the tool shaft coupler  15  (e.g.,  55 ′ and  67  respectively in FIG.  3 A), maximum axial movement of the mating tool shaft with respect to the driving shaft under an axial load alternating between tension and compression. 
     Preferred embodiments of a mating tool shaft (e.g.,  50 ′ in FIG. 3A) comprise at least one tension transmission surface (e.g.,  53 ′ in FIG. 3A) spaced apart from one of said at least one compression transmission surface (e.g.,  55 ′ in FIG. 3A) about 0.223 inches (e.g., illustrated by the distance X′ in FIG.  3 A). In embodiments of the present invention using alternate compression transmission surfaces (e.g.,  57 ′ and  67 ′ in FIG.  3 A), a tension transmission surface such as  53 ′ in FIG. 3A is preferably spaced apart from compression transmission surface  57 ′ a distance X″ which is less than the above spacing (of about 0.223 inches) but provides substantially the same limitation on maximum axial movement of the mating tool shaft ( 50 ′ in FIG.  3 A). 
     Note that a compression transmission surface of the present invention, whether coupled to driving shaft  60  or on a mating tool shaft, may have substantially the same shape as the portion of mating tool shaft  50 ′ illustrated in cross-section in FIG. 3C, i.e., the cross-section may be substantially semicircular. In preferred embodiments of mating tool shafts  50 , 50 ′, one or more warning bands  99 ′ of distinctive visual appearance may be applied to the portion of a mating tool shaft surface adjacent to and just concealed by the attachment means  17  when the mating tool shaft is drivingly engaged with the tool shaft coupler  15  (as in FIG.  1 B). Because such driving (effective) engagement implies sliding insertion of the mating tool shaft  50 , 50 ′ within the coupler  15  to an effective depth wherein all corresponding axial force and torque transmission surfaces on the mating tool shaft and in the coupler are substantially fully engaged, faulty engagement of the force transmission surfaces occurs when the mating tool shaft is inserted in the coupler to a depth less than the effective depth. Insertion of a mating tool shaft  50 , 50 ′ to a less-than-effective depth will then leave at least part of a visually distinctive portion  99 ′ on the mating tool shaft unconcealed by the attachment means (as in FIG.  1 A), thus providing a visual warning of the tool shaft&#39;s improper insertion into the coupler  15 . 
     The present invention also comprises a method (schematically illustrated as a flow chart in FIG. 2) of reversibly coupling a driving shaft and a mating tool shaft, the method comprising (step  101 ) ascertaining that the driving and mating tool shafts have corresponding driving shaft and mating tool shaft torque transmission surfaces drivingly attached to (or an integral part of) the driving and mating tool shafts respectively to transmit torque between the driving and mating tool shafts; (step  103 ) ascertaining that the driving and mating tool shafts have corresponding driving shaft and mating tool shaft compression transmission surfaces drivingly attached to (or an integral part of) the driving and mating tool shafts respectively to transmit axial compressive forces between the driving and mating tool shafts; (step  105 ) ascertaining that the driving and mating tool shafts have corresponding driving shaft and mating tool shaft tension transmission surfaces drivingly attached to (or an integral part of) the driving and mating tool shafts respectively to transmit axial tension forces between the driving and mating tool shafts, said driving shaft tension transmission surface being spaced apart from said driving shaft torque transmission surface, and said mating tool shaft tension transmission surface being spaced apart from said mating tool shaft torque transmission surface; (step  107 ) reversibly unlocking a movable tension-resisting member, allowing movement of said member out of a tension-resisting position between said corresponding driving shaft and mating tool shaft tension transmission surfaces; (step  109 ) effectively engaging the driving shaft with the mating tool shaft so that respective corresponding portions of torque transmission surfaces, tension transmission surfaces, and compression transmission surfaces of the driving and mating tool shafts are proximate; (step  111 ) reversibly moving a movable tension-resisting member into a tension-resisting position between said corresponding driving shaft and mating tool shaft tension transmission surfaces for transmitting axial tension force between said driving shaft and said mating tool shaft by compression of said tension-resisting member; (step  113 ) reversibly locking said movable tension-resisting member into said tension-resisting position with a shaft locking means; and (step  115 ) providing a visual indicator for indicating malfunction of the shaft locking means as described herein.