Patent Publication Number: US-6702090-B2

Title: Power tool and spindle lock system

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part of application Ser. No. 09/995,256, filed Nov. 27, 2001, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to power tools and, more particularly, to a spindle lock system for a power tool. 
     BACKGROUND OF THE INVENTION 
     A typical electric machine, such as a rotary power tool, includes a housing, a motor supported by the housing and connectable to a power source to operate the motor, and a spindle rotatably supported by the housing and selectively driven by the motor. A tool holder, such as a chuck, is mounted on the forward end of the spindle, and a tool element, such as, for example, a drill bit, is mounted in the chuck for rotation with the chuck and with the spindle to operate on a workpiece. 
     To assist the operator in removing and/or supporting the tool element in the tool holder, the power tool may include a spindle lock for preventing rotation of the spindle relative to the housing when a force is applied by the operator to the tool holder to remove the tool element. Without the spindle lock, such a force would tend to rotate the spindle relative to the housing. The spindle lock may be a manually-operated spindle lock, in which the operator engages a lock member against the spindle to prevent rotation of the spindle, or an automatic spindle lock, which operates when a force is applied by the operator to the tool holder. 
     There are several different types of automatic spindle locks. One type of automatic spindle lock includes a plurality of wedge rollers which are forced into wedging engagement with corresponding wedge surfaces when a force is applied by the operator to the tool holder. Another type of automatic spindle lock includes inter-engaging toothed members, such as a fixed internally-toothed gear and a movable toothed member supported on the spindle for rotation with the spindle and for movement relative to the spindle to a locked position in which the teeth engage to prevent rotation of the spindle. 
     To accommodate such automatic spindle locks, some rotational play or movement may be provided between the spindle and the driving engagement with the motor. The spindle lock operates (is engaged and disengaged) within this “free angle” of rotation between the spindle and the driving engagement of the motor. 
     SUMMARY OF THE INVENTION 
     One independent problem with the above-identified automatic spindle locks is that, when the motor is switched from an operating condition, in which the spindle is rotatably driven, to a non-operating condition, the inertia of the still-rotating spindle (and tool holder and/or supported tool element) causes the automatic spindle lock to engage to stop the rotation of the spindle relative to the motor within the free angle of rotation between the spindle and the motor. The engagement of the spindle lock can be sudden, causing an impact in the components of the spindle lock, resulting in noise (a big “clunk”) and, potentially, damage to the components. 
     This problem is increased the greater the inertia acting on the spindle (i.e., with larger tool elements, such as hole saws). With the high-inertia tool elements, the spindle may rebound from the impact (of the spindle lock engaging), rotate in the opposite direction (through the free angle of rotation) and impact the driving engagement with the motor, and rebound (in the forward direction) to re-engage the spindle lock. Such repeated impacts on the spindle lock and between the spindle and the driving engagement of the motor causes a “chattering” phenomenon (multiple noises) after the initial impact and big “clunk”. 
     Another independent problem with existing power tools is that, when the motor is switched from the operating condition to the non-operating condition, a braking force may be applied to the motor while the spindle (under the force of the inertia of the spindle (and tool holder and/or supported tool element) continues to rotate through the free angle. The braking of the motor (coupled with the continued rotation of the spindle) causes the automatic spindle lock to engage resulting in noise (a big “clunk” and/or “chattering”) and, potentially, damage to the components. 
     The braking force applied to the motor can result from dynamic braking of the motor, such as by the operation of a dynamic braking circuit or as results in the operation (stopping) of a cordless (battery-powered) power tool. In other words, when the motor is stopped, the difference between the force rotating the spindle (the inertia of the spindle (and tool holder and/or supported tool element) and the force stopping the motor (i.e., whether the motor coasts or is braked) causes the automatic spindle lock to engage. The greater difference in these oppositely acting forces, the greater the impact(s) (a big “clunk” and/or “chattering”) when the spindle lock engages. 
     The present invention provides a power tool and a spindle lock system which substantially alleviates one or more of the above-described and other problems with existing power tools and spindle locks. In some aspects, the invention provides a spindle lock including a spring element for delaying operation of the spindle lock and a detent arrangement defining a position corresponding to a run position of the power tool and a position corresponding to a locked position of the spindle lock. In one rotational direction (i.e., the forward direction), a projection is positioned in first recess to provide an unlocked position and in a second recess to provide the locked position. In the opposite rotational direction (i.e., the reverse direction), the projection is positioned in the second recess to provide the unlocked position and in the first recess to provide the locked position. 
     In some aspects, the invention provides a spindle lock including a spring element which applies substantially equal spring force to delay the operation of the spindle lock when the spindle is rotated in the forward direction or in the reverse direction. In some aspects, the invention provides two spring members which cooperate to apply the substantially equal force to delay the operation of the spindle lock when the spindle is rotated in the forward direction or in the reverse direction. 
     In some aspects, the spindle lock is a wedge roller type spindle lock. In some aspects, the invention provides a spindle lock including a synchronization member for synchronizing the engagement of the locking members and the locking surfaces of the spindle lock. In some aspects, the invention provides a spindle lock having an aligning member for aligning the axis of the wedge roller with the axis of the spindle and maintaining such an alignment. In some aspects, the invention provides a battery-powered tool including a spindle lock. 
     One independent advantage of the present invention is that stopping of the motor and automatic locking of the spindle can be done quietly without producing the impact or “clunk” accompanied by the sudden engagement of the spindle lock. The resilient force of the spring element of the spindle rotation controlling structure buffers and controls the rotation of the spindle caused by the inertia of the spindle (and tool holder and/or supported tool element). This resilient force also buffers and controls the inertia of the spindle when there is little or no relative rotation between the spindle and the driving engagement with the motor. 
     Another independent advantage of the present invention is that, even if the inertia of the spindle, tool holder and supported tool element is greater than the resilient force of the spring element of the spindle rotation controlling structure (such that the rotation of the spindle does not stop immediately upon the initial engagement of the spindle lock), the spring element buffers and controls the rotation of the spindle to dissipate the rotating energy of the spindle without the repeated impacts and rebounds or “chattering”, providing a more quiet stopping of the spindle. 
     A further independent advantage of the present invention is that, even when the motor is braked at stopping, such as by the operation of a braking circuit or in the operation of a cordless power tool, the spindle lock and the spring element of the spindle rotation controlling structure will quietly stop the rotation of the spindle, tool holder and tool element. 
     Other independent features and independent advantages of the present invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a cordless power tool including a spindle lock system embodying the invention. 
     FIG. 2 is a side view of a corded power tool including a spindle lock system embodying the invention. 
     FIG. 3 is a partial cross-sectional side view of a portion of the power tool shown in FIG.  1  and illustrating the spindle lock system embodying the present invention. 
     FIG. 4 is an enlarged cross-sectional side view of a portion of the spindle lock system shown in FIG.  3 . 
     FIG. 5 is an exploded view of the components of the spindle lock system shown in FIG.  4 . 
     FIG. 6 is a view of the components of the spindle lock system shown in FIG.  5 . 
     FIG. 7 is a partial cross-sectional view of components of the spindle lock system. 
     FIG. 8 is a partial cross-sectional view illustrating the connection of the spindle with the carrier. 
     FIG. 9 is an exploded partial cross-sectional side view of a torque limiter. 
     FIG. 10 is a view of a first alternative construction of the supporting ring. 
     FIG. 11 is a view of a second alternative construction of the supporting ring. 
     FIG. 12 is an enlarged partial cross-sectional side view of a first alternative construction of the rotation controlling structure of the spindle lock system taken generally along line C-C′ in FIG.  14 . 
     FIG. 13 is an exploded partial cross-sectional view of the rotation controlling structure shown in FIG.  12 . 
     FIG. 14 is a partial cross-sectional view taken generally along line A-A′ in FIG.  12 . 
     FIG. 15 is a partial cross-sectional view taken along line B-B′ in FIG.  12 . 
     FIG. 16 is a partial cross-sectional view of a second alternative construction of the rotation controlling structure of the spindle lock system. 
     FIG. 17 are partial cross-sectional views of a portion of the spindle lock system shown in FIG.  16 . 
     FIG. 18 is a partial cross-sectional view of an alternative construction of the locking structure of the spindle lock system. 
     FIG. 19 is a partial cross-sectional view of the spindle lock system shown in FIG.  18  and illustrating the operating condition of the spindle lock system. 
    
    
     Before one embodiment of the invention is explained in detail, it is to be understood that the invention is not limited in its application to the details of the construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a power tool  100  including (see FIG. 3) a spindle lock system  10  embodying the invention. As shown in FIG. 1, the power tool  100  includes a housing  104  having a handle  108  to be gripped by an operator during operation of the power tool  100 . A motor M (schematically illustrated) is supported by the housing  104 , and a power source  112 , such as, in the illustrated construction, a battery  116 , is connectable to the motor M by an electrical circuit (not shown) to selectively power the motor M. 
     The power tool  100  also includes a spindle  28  rotatably supported by the housing  104  and selectively driven by the motor M. A tool holder or chuck  120  is supported on the forward end of the spindle  28  for rotation with the spindle  28 . A tool element, such as, for example, a drill bit  124 , is supported by the chuck  120  for rotation with the chuck  120 . 
     In the illustrated construction, the power tool  100  is a drill. It should be understood that, in other constructions (not shown), the power tool  100  may be another type of power tool, such as, for example, a screwdriver, a grinder or a router. It should also be understood that, in other constructions (not shown), the tool element may be another type of tool element, such as, for example, a screwdriver bit, a grinding wheel, a router bit or a hole saw. 
     FIG. 2 illustrates another power tool  200  for use with the spindle lock  10 . As shown in FIG. 2, the power tool  200  is a corded power tool including a housing  204  providing a handle  208  and supporting a motor M′ (schematically illustrated) which is connectable to an AC power source  212  by a plug  216  to selectively power the motor M′. 
     As shown in FIG. 3, the motor M includes an output shaft  11   a  defining a motor axis  11  and rotatably supported by the housing  104 . In the illustrated construction, the motor M is connected to a speed reduction structure  12  of a planetary gear. The speed reduction structure  12  includes a sun gear  13  connected by an attaching structure, such as splines, to the output shaft  11   a  for rotation with the output shaft  11   a . The speed reduction structure  12  also includes a planetary gear  14  supported by a carrier  15  and engageable between the sun gear  13  and an internal gear  16 . The internal gear  16  is supported by a fixing ring  17  which is supported by the housing  104 . Rotation of the motor shaft  11   a  and the sun gear  13  causes rotation of the planet gear  14 , and engagement of the rotating planet gear  14  with the internal gear  16  causes the planet gear  14  to revolve around the sun gear  13  and rotation of the carrier  15 . 
     The spindle lock system  10  is supported on the outputting side of the motor M (on the outputting side of the speed reduction structure  12 ). The spindle lock system  10  includes a driving engagement or an output electric structure  10 ′ for conveying the output force of the motor M, through the carrier  15  of the speed reduction structure  12 , to the spindle  28 . The spindle lock system  10  also includes locking structure  10 ″ for locking the spindle  28  and selectively preventing rotation of the spindle  28  relative to the housing  104  and relative to the carrier  15  and motor M. 
     As shown in more detail in FIGS. 4 and 8, the driving engagement  10 ′ between the spindle  28  and the carrier  15  and motor M includes a connector  31  formed on the end of the spindle  28  (as two generally parallel planar surfaces on opposite sides of the spindle axis) and a hole-shaped connector  32  formed on the carrier  15 . The connector  32  has sidewalls which are formed to provide a free angle α (of about 20 degrees in the illustrated construction) in which the spindle  28  and the carrier  15  are rotatable relative to one another to provide some rotational play between the spindle  28  and the carrier  15 . When the connecting parts  31  and  32  are connected, there is a free rotational space in which the carrier  15  will not convey rotating force to the spindle  28  but in which the carrier  15  and the spindle  28  are rotatable relative to one another for the free angle α. In the illustrated construction, the shape of the connector  32  provides this free play in both rotational directions of the motor M and spindle  28 . 
     As shown in FIGS. 4-6, the locking structure  10 ″ generally includes a release ring  21 , a spring or snap ring  22 , two synchronizing and aligning or supporting rings  23 , one or more locking members or wedge rollers  24 , a lock ring  25 , a rubber ring  26 , a fixing ring  27  and the spindle  28 . Except for the wedge rollers  24  and the spindle  28 , the other components of the locking structure  10 ″ are generally in the shape of a ring extending about the same axis, such as the axis of the spindle  28 . A lid ring  45  is attached to the fixing ring  27  such that the components of the locking structure  10 ″ are provided as a unit. 
     As shown in FIGS. 4-5, the release ring  21  includes pins  33  on opposite sides of the axis which are engaged and retained in connecting holes  34  formed on the carrier  15  so that the release ring  21  is fixed to and rotatable with the carrier  15 . As shown in FIG. 6, the release ring  21  defines a hole-shaped connector  32   a  which is substantially identical to the connector  32  formed in the carrier  15  to provide the free rotational angle α between the spindle  28  and the carrier  15  and release ring  21 . 
     The lock ring  25  defines a hole-shaped connecting part  35  which is substantially identical to the connector  31  on the spindle  28  so that the lock ring  25  is fixed to and rotatable with the spindle  28  without free rotational movement. On the outer circumference, the lock ring  25  includes dividing protrusions  36  which, in the illustrated construction, are equally spaced from each other by about 120 degrees. On each circumferential side of each protrusion  36 , inclined locking wedge surfaces  37   a  and  37   b  are defined to provide locking surfaces so that the spindle lock system  10  will lock the spindle  28  in the forward and reverse rotational directions. The wedge surfaces  37   a  and  37   b  are inclined toward the associated protrusion  36 . 
     In the illustrated construction, the locking members are wedge rollers  24  formed in the shape of a cylinder. A wedge roller  24  is provided for each locking wedge surface  37   a  and  37   b  of the lock ring  25 . The wedge rollers  24  are provided in three pairs, one for each protrusion  36 . One wedge roller  24  in each pair provides a locking member in the forward rotational direction of the spindle  28 , and the other wedge roller  24  in the pair provides a locking member in the reverse rotational direction of the spindle  28 . In the illustrated construction, the length of each wedge roller  24  is greater than the width or thickness of the lock ring  25 , and the opposite ends of each wedge roller are supported by respective supporting rings  23 . 
     On the outer circumference of each supporting ring  23 , supporting protrusions  38  are formed. In the illustrated construction, the supporting protrusions  38  are equally separated by about 120 degrees, and on each side of each supporting protrusion  38 , a wedge roller  24  is supported. As shown in FIG. 6, the central opening of each supporting ring  23  is generally circular so that the supporting rings  23  are rotatable relative to the spindle  28 . 
     The rubber ring  26  is supported in a groove in the fixing ring  27 , and engagement of the wedge rollers  24  with the rubber ring  26  causes rotation of the wedge rollers  24  due to the friction between the wedge rollers  24  and the rubber ring  26 . The fixing ring  27  defines an inner circumference or cavity  39  receiving the lock ring  25  and the supporting rings  23 . The inner circumference  39  of the fixing ring  27  and the outer circumference of the lock ring  25  (and/or of the spindle  28 ) face each other in a radial direction and are spaced a given radial distance such that a pair of wedge rollers  24  are placed between a pair of inclined locking wedge surfaces  37   a  and  37   b  of the lock ring  25  and the inner circumference  39 . 
     The inclined locking wedge surfaces  37   a  and  37   b  and the inner circumference  39  of the fixing ring  27  cooperate to wedge the wedge rollers  24  in place in a locked position which corresponds to a locked condition of the spindle lock system  10 , in which the spindle  28  is prevented from rotating relative to the housing  104  and relative to the motor M and carrier  15 . Space is provided between the inner circumference  39  of the fixing ring  27  and the outer circumference of the lock ring  25  to allow the wedge rollers to move to a releasing or unlocked position which corresponds to an unlocked condition of the spindle lock system  10 , in which the spindle  28  is free to rotate relative to the housing  104 . In addition, the supporting protrusions  38  of the supporting rings  23  have a circumferential dimension allowing the wedge rollers  24  to be supported in the releasing or unlocked position. 
     The releasing ring  21  includes releasing protrusions  41  which are selectively engageable with the wedge rollers  24  to release or unlock the wedge rollers  24  from the locked position. The releasing protrusions  41  are formed on the forward side of the releasing ring  21  and, in the illustrated construction, are equally separated by about 120 degrees to correspond with the relative position of the three pairs of wedge rollers  24 . Each releasing protrusion  41  is designed to release or unlock the associated wedge rollers  24  by engagement with the circumferential end part to force the wedge roller  24  in the direction of rotation of the releasing ring  21  (and the carrier  15  and motor M). The circumferential length of each releasing protrusion  41  is defined so that the releasing or unlocking function is accomplished within the free rotational angle α between the spindle  28  and the releasing ring  21  and the carrier  15 . Preferably, the releasing or unlocking function is accomplished near the end of the free rotational angle α. 
     Each releasing protrusion  41  defines one portion of a detent arrangement or controlling structure for controlling the resilient force of the snap ring  22  between a detent position corresponding to an unlocked condition of the spindle lock system  10  and a detent position corresponding to the locked condition of the spindle lock system  10 . In the illustrated construction, controlling concave recesses  42   a  and  42   b  are defined on the radially inward face of each releasing protrusion  41 . 
     As shown in FIGS. 6-7, the snap ring  22  includes spring or snap arms  44  each having a controlling convex projection  43  formed at its free end. The projections  43  provide the other portion of the detent arrangement and are selectively engageable in one of a pair of corresponding recesses  42   a  and  42   b . The snap ring  22  provides a resilient force to bias the projections into engagement with a selected one of the recesses  42   a  and  42   b . The snap arms  44  are formed as arcuate arms extending generally in the same direction about the circumference from three equally separated positions on the body of the snap ring  22 . The snap arms  44  are formed so that the projections  43  are selectively positionable in the associated recesses  42   a  and  42   b . The resilient spring force on the projections  43  is provided by the elasticity and material characteristics of the snap arms  44 . 
     The resilient force of the snap ring  22  is smaller than the drive force of the motor M and will allow the projections to move from one recess (i.e., recess  42   b ) to the other recess (i.e., recess  42   a ), when the motor M is restarted. As shown in FIG. 6, the central opening of the snap ring  22  is substantially identical to the connector  31  of the spindle  28  so that the snap ring  22  is fixed to and rotates with the spindle  28 . The resilient force the snap arms  44  apply to the projections  43  is set to allow the projection  43  to move from one recess (i.e., recess  42   a ) to the other recess (i.e., recess  42   b ) to control and buffer the rotational force of the spindle  28  when the motor M is stopped and to delay the engagement of the locking structure  10 ″. 
     As shown in FIGS. 3 and 9, the speed reduction structure  12  is provided with a torque limiter. The internal gear  16  is supported to allow rotation relative to the fixing ring  17 . The forward end of the internal gear  16  provides an annular surface  50 . Balls  51  are pressed against the surface  50 , and the internal gear  16  is pressed against a fixing plate  52  to prevent the internal gear  16  from rotating. 
     A plurality of balls  51  (six in the illustrated construction) are positioned about the circumference of the internal gear  16  in engagement with the surface  50 . A fixing element  53  defines a hole  54  for each ball  51  and received the ball  51  and a biasing spring  55 . The spring  55  presses the ball  51  against the surface  50  of the internal gear  16  so that the internal gear  16  is pressed against the fixing plate  52 . A receiving element includes supporting pins  57  which support the respective springs  55 . 
     The forward end of the fixing element  53  is formed with a screw  58 . A nut  59  engages the screw thread  58  and axially moves, through the ball  60  and ring  61 , the receiving element towards and away from the internal gear  16  to adjust the spring force applied by the springs  55  to the balls  51  and to the surface  50  of the internal gear  16 . The nut  59  is connected to an operating cover  62  by a spline attachment, and rotation of the operating cover  62  causes rotation and axial movement of the nut  59 . 
     The fixing ring  27  is fixed to the fixing element  53  through a retaining part  64  to prevent rotation of the fixing ring  27 . Alternatively, the retaining part  64  may be formed in the shape of a pin to be inserted into a hole in the fixing element  53 . The fixing plate  52 , the fixing ring  17  and the fixing element  53  are fixed to the outer case  63  of the housing  104 . 
     In operation, when the carrier  15  and the releasing ring  21  are rotated in the direction of arrow X (in FIG. 7) by operation of the motor M, the corresponding wedge roller  24   a  is pushed into a releasing or unlocked position of the inclined surface  37   a  of the lock ring  25  by the end of the releasing protrusion  41 . The other wedge roller  24   b  is kept in contact with the inner circumference  39  of the fixing ring  27 , and, by its frictional contact, the wedge roller  24   b  is pushed into the releasing position of the inclined surface  37   b . This releasing or unlocking function is accomplished within the free rotational angle α between the spindle  28  and the carrier  15  and the motor M. 
     After the locking structure  10 ″ is released or unlocked, the connecting part  32  of the carrier  15  and the connecting part  31  of the spindle  28  move into driving engagement so that the driving force of the carrier  15  (and motor M) is transferred to the spindle  28  and the spindle  28  rotates with the carrier  15 . At this time, each projection  43  of each snap arm  44  is positioned in one recess (i.e., recess  42   a , the “run” position recess) of each releasing protrusion  41 , and the position of the releasing ring  21  and the lock ring  25  is controlled by the resilient force of the snap arms  44  in a releasing or unlocked position at one end of the free angle α. 
     During driving operation of the motor M, the releasing protrusion  41  provides a force necessary to push the wedge roller  24   a  into the releasing or unlocked position and does not provide a large impact force on the wedge rollers  24   a . When the motor M is stopped (switched from the operating condition to the non-operating condition) rotation of the carrier  15  is stopped. Rotation of the spindle  28  is controlled and buffered by the resilient force of the snap arms  44  retaining the projection  43  in the selected recess (i.e., recess  42   a ). During stopping, if the inertia of the spindle  28  (and the chuck  120  and/or the supported bit  124 ) is less than the resilient force of the snap arms  44 , rotation of the spindle  28  is stopped with the projections  43  being retained in the selected recess (i.e., recess  42   a , the run position). In such a case, the resilient force of the snap ring  22  buffers and controls the inertia of the spindle  28  even when there is little or no relative rotation between the spindle  28  and the carrier  15  and the motor M. 
     When the inertia of the spindle  28  (and the chuck  120  and/or the bit  124 ) is greater than the resilient force of the snap arms  44 , the inertia overcomes the resilient force of the snap arms  44  and the friction between the projections  43  and the inclined ramp surface adjacent to the selected recess  42   a  so that the projections  43  move from the recess  42   a  and to the other recess  42   b  (the “lock” position recess). Movement of the projections  43  from recess  42   a  and to the recess  42   b  resists the rotational inertia of the spindle  28  and controls and buffers the rotational inertia of the spindle  28  so that the rotation of the spindle  28  will be dissipated before the locking structure  10 ″ engages. 
     Therefore, the rotational inertia of the spindle  28  (and the chuck  120  and/or bit  124 ) is controlled and buffered by the engagement of the projections  43  in the respective recesses  42   a  and movement to the recesses  42   b  under the resilient spring force applied the respective snap arms  44 . The snap ring  22  controls the rotational force of the spindle  28  and delays the engagement of the wedge rollers  24  and the locking wedge surfaces  37  so that there is no impact in the components of the spindle lock system  10 , and no noise (no big “clunk”) is created when the rotation of the spindle  28  has stopped. Also, because the rotational force of the spindle  28  is controlled, there is no impact of the spindle lock and rebound through the free rotational angle α so that the “chattering” phenomenon is also avoided. The rotational control device of the spindle lock system  10  includes the detent arrangement provided by the recesses  42   a  and  42   b  and the projections  43  and the resilient spring force provided by the snap arms  44  of the snap ring  22 . 
     When the operator operates the chuck  120  (which tends to rotate the spindle  28  relative to the carrier  15  and motor M), rotation of the spindle  28  will be prevented because of the functioning of the locking structure  10 ″. When the operator attempts to rotate the spindle  28  (i.e., by operating the chuck  120 ), the wedge rollers  24  will be wedged between the inner circumference  39  of the fixing ring  27  and the respective inclined locking wedge surfaces  37   a  and  37   b  of the lock ring  25  so that rotation of the spindle  28  in each rotational direction will be prevented. Because the spindle  28  is prevented from rotating, the chuck  120  can be easily operated to remove and/or support the bit  124 . 
     When the motor M is restarted (switched from the non-operating condition to the operating condition, the end of the releasing protrusion  41  (in the selected rotational direction) moves one wedge roller  24   a  to a releasing position. The other wedge roller  24   b  engages the inner circumference  39  of the fixing ring  27  and is pushed into a releasing position. Once the wedge rollers  24  are released, the spindle  28  is free to rotate. The spindle  28  begins to rotate under the force of the motor M at the end of the free angle α of rotation between the spindle  28  and the carrier  15  and motor M. 
     When the spindle  28  is driven and the wedge rollers  24  rotate about their respective axes and revolve about the spindle  28 , the wedge rollers  24  are kept in contact with the rubber ring  26 , and this contact resistance causes the wedge rollers  24  to rotate while revolving. This rotation of the wedge rollers  24  and engagement with the supporting protrusions  38  of the supporting rings  23  on a trailing portion of the respective wedge rollers  24  maintains the respective axes of the wedge rollers  24  in an orientation in which the roller axes are substantially parallel to the axis of the spindle  28 . 
     Engagement of the supporting protrusions  38  of the supporting rings  23  with the trailing portion of the respective wedge rollers  24  during movement of the wedge rollers  24  from the unlocked position toward the locked position prevents the wedge rollers  24  from becoming misaligned. Preferably, the supporting protrusions  38  engage the trailing portion of the respective wedge rollers  24  from the unlocked position, to the locked position and in the locked position. 
     The supporting rings  23  thus provide an aligning feature for the wedge rollers  24 . Because the roller axes are aligned with the axis of the spindle  28 , when the wedge rollers are wedged between the inner circumference  39  of the fixing ring and the inclined wedge surfaces  37  of the lock ring  25 , a line contact is provided between the wedge rollers  24  and these locking surfaces to provide maximum locking force. The supporting rings  23  also provide a synchronizing feature of the wedge rollers  24  so that the wedge rollers  24  simultaneously move to the locking position upon engagement of the locking structure  10 ″. 
     FIG. 10 illustrates a first alternative construction for a supporting ring  23 A. Common elements are identified by the same reference number “A”. 
     In the earlier-described construction, the wedge rollers  24  are supported in the releasing position by the supporting protrusions  38  of the supporting ring  23 . In the first alternative construction (shown in FIG.  10 ), the wedge rollers  24 A are supported by concave parts  71   a  and  71   b  of an elastic material  71 . Preferably, the elastic material  71  is formed of a flexible elastic material such as a spring material. A concave base  72  connects the parts  71   a  and  71   b  and is connected to the supporting ring  23 A. 
     In the position shown in FIG. 10, the wedge rollers  24 A are supported in a releasing position in close proximity to the locked position of each wedge roller  24 A. The elastic member  71  supports the wedge rollers  24 A with flexibility so that the wedge rollers  24 A may flex the concave parts  71   a  and  71   b  to move towards a further released position. When the releasing protrusion  41 A engages the wedge rollers  24 A to release or unlock the wedge rollers  24 A, the flexible elastic member  71  attenuates any resulting shock. 
     During driving of the spindle  28 A, the leading concave parts  71   a  or  71   b  (depending on the driving direction of the spindle  28 A) are compressed so that the trailing portion of the respective leading wedge rollers  24 A are engaged by the respective concave parts  71   a  or  71   b  and by the dividing protrusions  36 A on the lock ring  25 A. When the motor M is stopped, the concave parts  71   a  or  71   b  expand and cause an initial locking engagement with the respective wedge rollers  24 A. The expanding concave parts  71   a  or  71   b  also maintain engagement with the trailing portion of the respective wedge rollers  24 A as the wedge rollers  24 A move from the unlocked position toward the locked position. Preferably, the concave parts  71   a  or  71   b  maintain engagement with the trailing portion of the respective wedge rollers  24 A as the wedge rollers  24 A move from the unlocked position, to the locked position and in the locked position. This engagement prevents the wedge rollers  24 A from becoming misaligned. 
     In this construction, the center opening of the supporting ring  23 A is formed with a connecting part which is substantially identical to the connecting part  31 A of the spindle  28 A so that the supporting ring  23 A is fixed to and rotatable with the spindle  28 A. However, in an alternative construction (not shown), the central opening of the supporting ring  23 A may be circular. 
     FIG. 11 illustrates a second alternative construction of a supporting ring  23 B. Common elements are identified by the same reference number “B”. 
     In the first alternative construction shown in FIG. 10, elastic material  71  was connected to the body of the supporting ring  23 A. In the construction illustrated in FIG. 11, the supporting ring  23 B includes arms  73  providing concave part  74   a  and  74   b  at their ends to provide a flexible support for the wedge rollers  24 B. With the construction illustrated in FIG. 11, the supporting ring  23 B with the elastic arms  73  provides the same operation as concave parts  71   a  and  71   b  of the supporting ring  23 A illustrated in FIG.  10 . 
     In the illustrated construction, the central opening of the supporting ring  23 B is substantially identical to the connecting part  32 B of the carrier  15 B. As with the other supporting rings  23  and  23 A, the central opening may be circular or may have the shape of the connecting part  31  of the spindle  28 . In any of these constructions, the supporting ring  23 ,  23 A and  23 B may be formed of a metal plate or a synthetic resin. 
     FIGS. 12-15 illustrate a first alternative construction of the rotation control device of a spindle lock  10 C. Common elements are identified by the same reference number “C”. 
     As shown in FIGS. 12-15, the rotation control device includes a snap ring  22 C formed by two snap ring elements  22 C a  and  22 C b . The snap ring elements  22 C a  and  22 C b  are substantially identical and are supported in a reversed orientation relative to one another to provide the snap ring  22 C. 
     In this construction, the forward end of the carrier  15 C defines the control concave recesses  42 C a  and  42 C b  for receiving the control convex projections  43 C a  and  43 C b  on each of the snap ring elements  22 C a  and  22 C b  to provide the controlling and buffering of the continued rotation of the spindle  28 C. The forward end of the carrier  15 C includes a containing recess  82  having an inner circumference  81  receiving the two snap ring elements  22 C a  and  22 C b . The recesses  42 C a  and  42 C b  are formed at three circumferentially spaced locations which correspond to the position of the recesses  42   a  and  42   b  in the earlier-described construction. 
     The snap rings  22 C a  and  22 C b  are received in the containing recess  82  to form the snap ring  22 C. Each snap ring element  22 C a  and  22 C b  has a snap ring body from which respective snap arms  44 C a  and  44 C b  extend. Corresponding projections  43 C a  and  43 C b  are formed at the end of each snap arm  44 C a  and  44 C b , respectively. In the illustrated construction, the snap ring elements  22 C a  and  22 C b  are supported so that the arms from one snap ring element (i.e., arms  44 C a  of snap ring  22 C a ) extend in one circumferential direction and the arms of the other snap ring elements (i.e., arms  44 C b  of snap ring  22 C b ) extend in the opposite circumferential direction. 
     The snap ring elements  22 C a  and  22 C b  are supported so that the corresponding projections  43 C a  and  43 C b  are aligned and are positioned in the same recess  42 C a  or  42 C b . In this manner, the snap ring  22 C provides the same force on the projections  43 C when a force is applied to the snap ring  22 C in either rotational direction by the spindle  28 C. Because of the configuration of the snap ring elements  22 C a  and  22 C b , in one rotational direction, one projection and snap arm (i.e., projection  43 C a  and snap arm  44 C a ) will apply a spring force to retain the projection  43 C a  in the selected recess, and this spring force will provide a first portion of the total spring force applied by the snap ring  22 C. At the same time, the other projection and snap arm (i.e., projection  43 C b  and snap arm  44 C b ) will apply a spring force to maintain the projection  43 C b  in the selected recess, and this spring force will provide a second portion of the total force applied by the snap ring  22 C. 
     In the opposite rotational direction, the first snap ring element  22 C a  will apply a first spring force which is a first portion of the total force applied by the snap ring  22 C, and the second snap ring element  22 C b  will apply a second spring force which is a second portion of the total force applied by the snap ring  22 C to control and buffer the rotation of the spindle  28 C in that rotational direction. Because of the configuration of the snap ring elements  22 C a  and  22 C b , the snap ring elements  22 C a  and  22 C b  apply a different force in each of the rotational directions when controlling and buffering the rotation of the spindle  28 C. However, in each rotational direction, the snap ring  22 C applies substantially the same spring force to control and buffer the rotation of the spindle  28 C. 
     It should be understood, that in the earlier-described construction (shown in FIGS.  2 - 7 ), the snap ring  22  could include two separate snap ring elements (similar to snap ring elements  22 C a  and  22 C b ). 
     As shown in FIG. 13, a guard-like annular portion  83  is formed on the rear face of the releasing ring  21 C, and retaining projections  84  are formed on the inner annular surface of the portion  83 . A step  85  is formed on the outer circumference of the carrier  15 C, and retaining recesses  86  are formed in locations about the step  85 . The projections  84  and the recesses  86  engaged to fix the releasing ring  21 C to the carrier  15 C as a unit. The snap ring  22 C and snap ring elements  22 C a  and  22 C b  are received in the space between the carrier  15 C and the releasing ring  21 C. 
     As shown in FIG. 14, the supporting ring  23 C is similar to the supporting ring  23 B and includes elastic arms  73 C to support the wedge rollers  24 C (maintaining their alignment and synchronizing their locking action). 
     As also shown in FIG. 14, the fixing ring  27 C defines retaining recesses  64 C which receive pins  87  connected to the fixing element  53 C to connect the fixing ring  27 C to the fixing element  53 C. Elastic material  88  is positioned between the recesses  64 C and the pins  87  to absorb any impact caused by the spindle lock  10 C engaging and preventing such an impact from being transferred from the fixing ring  27 C and to the fixing element  53 C. The elastic material  88  can be any type of rubber or elastic material to absorb an impact. 
     As shown in FIG. 15, the connecting part  35 C of the lock ring  25 C and the connecting part  31 C of the spindle  28 C are formed such that there is a free rotational angle β between the connecting part  31 C of the spindle  28 C and the connecting part  35 C of the locking ring  25 C. In the illustrated construction, this free rotational angle β is smaller (i.e., an angle of about 10 degrees) than the free rotational angle U (an angle of about 20 degrees) between the connecting part  32 C of the carrier  15 C and the connecting part  31 C of the spindle  28 C. The free rotational angle β allows the locking ring  25 C to be easily connected to the spindle  28  while maintaining the proper operation of the spindle lock  10 C. 
     FIGS. 16-17 show a second alternative construction of the rotation controlling structure of a spindle lock  10 D. Common elements are identified by the same reference number “D”. 
     In the illustrated construction, the rotational control structure includes a single recess  42 D for each projection  43 C (rather than the two recesses  42   a  and  42   b  of earlier-described constructions). Each recess  42 D is formed in a location corresponding to an unlocked position of the wedge rollers  24 D. As shown in more detail in FIG. 17, the recesses  42 D are formed on the dividing protrusion  36 D of the locking ring  25 D. In this construction, the snap ring  22 D includes two snap ring elements  22 D a  and  22 D b  supported in reversed orientations, and the snap ring  22 D (formed of snap ring elements  22 D a  and  22 D b ) engages the locking ring  25 D. 
     In operation, when the spindle  28 D is rotated relative to the driving engagement (the connection between the spindle  28 D and the carrier  15 D), the continued rotation of the spindle  28 D causes the projections  43 D to move from the recesses  42 D. The resilient force applied by the snap arms  44 D and this movement delays the engagement of the wedge rollers  24 D with the wedge surfaces defined by the locking ring  25 D and the fixing ring  27 D. 
     The snap ring  22 D controls and buffers the movement of the spindle  28 D and delays the movement of the wedge rollers  24 D and the locking ring  25 D to the locked position. In this construction, when the motor M is stopped and the spindle  28 D continues its rotation under inertia, the locking ring  25 D operates the wedge rollers  24 D (in the selected rotational direction) to lock the rotation of the spindle  28 D. The inertia of the spindle  28 D is controlled and buffered by the resilient force of the snap arms  44 D a  and  44 D b  so that there is no impact or “clunk” caused by a sudden stop when the spindle lock  10 D is engaged. Therefore, the spindle lock  10 D provides a quiet stop of the rotation of the spindle  28 D. Even if the inertia of the spindle  28 D is larger than can be buffered by the resilient force of the snap ring  22 D, the rotation of the spindle  28 D is stopped at an early stage so that there is no rebounding of the spindle  28 D and no “chattering”. 
     In this construction, the connecting part  35 D of the locking ring  25 D and the connecting part  31 D of the spindle  28 D also include a free rotational angle β, similar to that described above. 
     FIGS. 18-19 show an alternative construction of the locking structure  10 E′ of a spindle lock  10 E. Common elements are identified by the same reference number “E”. 
     In this construction, the locking structure  10 E′ includes locking elements, such as brake shoes  91 , which are engageable between the inner circumference  39 E of the fixing ring  27 E and the outer circumference of the locking ring  25 E to provide a locking and wedging action. Each brake shoe  91  is formed of a suitable frictional material, such as a metallic material, and the outer surface of each brake shoe  91  and the inner circumference  39 E of the fixing ring  27 E may be provided with inter-engaging projections and recesses, such as a serrated or pawl surfaces to provide a larger frictional resistance between the brake shoe  91  and the fixing ring  27 E. 
     Each brake shoe  91  includes a centrally-located inner cam  92 . On the outer circumference of the locking ring  25 D, a corresponding recess portion receives each projecting cam  92  (in the unlocked position of the brake shoe  91 ). Raised cam surfaces  93   a  and  93   b  are provided on each side of this recessed portion to engage the projecting cam  92  (in either rotational direction) to force the brake shoe  91  to the locked position, in which the brake shoe  91  engages the inner circumference  39 E of the fixing ring  27 E. 
     In the illustrated construction, continued rotation of the spindle  28 E, causes the locking ring  25 E to rotate so that, in the selected direction, the raised cam surfaces  93   a  and  93   b  engage the projecting cam  92  to press the brake shoe  91  against the inner circumference  39 E of the fixing ring  27 E to stop the rotation of the spindle  28 E. Locking and releasing of the brake shoes  91  is accomplished within the free rotational angle α between the spindle  28 E and the carrier  15 E. 
     A releasing protrusion  41 E is provided between each brake shoe  91 . The releasing protrusions  41 E are driven by the carrier  15 E and selectively engage the circumferential end portion of each brake shoe  91  to move the brake shoe  91  from the locked position to the unlocked position. On the circumferential end part of each releasing protrusion  41 E and brake shoe  91 , inter-engaging projections  95  and recesses  96  are formed. When these elements  95  and  96  are engaged, each brake shoe  91  is positioned in an unlocked position in which the outer circumference of the brake shoe  91  is radially spaced from the inner circumference  39 E of the fixing ring  27 E. 
     Each brake shoe  91  also includes a centrally-located axially-extending pin  94 . The supporting ring  23 E (which rotates with the spindle  28 E) includes a pair of arms  73 E which receive the pin  94 . Recesses  97  are formed in each arm  73 E for retaining the pin  94  in a unlocked position in which the outer circumference of the brake shoe  91  is spaced from the inner circumference  39 E of the fixing ring  27 E. 
     From the locked position of the locking structure  10 E′, the motor M is operated so that the carrier  15 E moves the releasing protrusions  41 E to engage the elements  95  and  96  and move the brake shoe  91  to the unlocked position. During this movement, the pin  94  is moved to engage the retaining recesses  97  formed between the arms  73 E of the supporting ring  23 E, and the brake shoe  91  is thus retained in the unlocked position radially spaced from the inner circumference  39 E of the fixing ring  27 E. The brake shoe  91  is retained in this unlocked position by engagement on one end by the releasing projection  41 E and at the center by engagement of the pin  94  with the retaining recesses  97 . In this unlocked position, because the brake shoes  91  are retained in a radially spaced position from the inner circumference  39 E of the fixing ring  27 E, there will not be inadvertent engagement of the brake shoe  91  with the fixing ring  27 E so that no “scraping” sound will result during driving of the spindle  28 E. 
     It should be understood, that in some aspects of the invention, the locking device  10 ″ may include the wedge roller-type locking assembly, the brake shoe assembly or some other type of locking assembly. 
     It should be understood that, in some constructions (not shown), the controlling force applied by the snap ring  22  to maintain the projection  43  in the selected recess  42  may be applied in another direction (i.e., radially-inwardly or axially). It should also be understood that, in other constructions (not shown), the projection  43  may be formed separately from but engageable with the snap arm  44  so that the snap arm  44  applies a force to engage the projection  43  in the selected recess  42 . 
     In accordance with the present invention, the resilient force provided by the rotation controlling device (including the snap ring  22  and the engagement between the projection  43  and the selected recess  42 ) controls and buffers the rotational inertia of the spindle  28  (and the chuck  120  and/or supported bit  124 ). 
     When the rotational inertia of the spindle  28  (and the chuck  120  and/or supported bit  124 ) is large, the resilient force applied by the snap ring  22  controls and buffers this increased rotational inertia so that no impact or “clunk” is caused when the spindle lock  10  engages to stop the rotation of the spindle  28 . 
     When the rotational inertia of the spindle  28  (and the chuck  120  and/or the drill bit  124 ) is much greater than the resilient force of the snap ring  22  and even when the spindle  28  may rebound, the resilient force of the snap ring  22  buffers the rotational inertia at an early stage in the continued rotation of the spindle  28 , greatly reducing this rotational force so that the spindle  28  does not impact and rebound and so that no “clunk” or “chattering” is caused during engagement of the spindle lock  10 . With the present invention, the spindle lock provides a quiet stopping of the spindle  28  (no “clunk” or “chattering”) and reduces any damage which might be caused to the components of the spindle lock  10  and the power tool. 
     The spindle lock  10  of the present invention provides for smooth constant locking and unlocking of the locking structure  10 ″ and smooth and constant operation of the power tool. 
     Various independent features of the present invention are set forth in the following claims.