Abstract:
A spindle lock ( 10 ) includes a detent arrangement including springs ( 25 ) acting on projections ( 30 ), each projection engaging one of a pair of recesses ( 40, 41 ) to control and buffer the rotation of a spindle ( 13 ) and to delay the engagement of locking elements ( 26   a,    26   b ). A compact, reliable mechanism with a high degree of modularity is achieved by providing the recesses in an inner rotor ( 31 ) and the springs and projections in an outer rotor ( 18 ) that extends about the inner rotor.

Description:
TECHNICAL FIELD 
     The present invention relates to power tools and, more particularly, to power tools with a lock for preventing rotation of the spindle. 
     BACKGROUND OF THE INVENTION 
     A typical rotary power tool includes a housing, a motor supported by the housing 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 a drill bit, is mounted in the chuck. 
     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. 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. 
     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. 
     U.S. Pat. No. 7,063,201 describes a power tool with a spindle lock that addresses these problems. The spindle lock includes a spring and a detent arrangement to control and buffer the rotation of the spindle and to delay the engagement of the locking elements in both forward and reverse operation. Multiple spring members may cooperate to apply a force to delay the operation of the spindle lock. However, one of the drawbacks that have been found to occur with this spindle lock is that the amount of delay can be variable. In addition, when producing a model range of power tools, it is advantageous to use common parts as far as possible, however with this old tool it has been difficult to readily vary the delay by changing the spring members alone, without a need to also alter the mutually engaged component parts. It is an object of the present invention to overcome or substantially ameliorate the above disadvantages or more generally to provide an improved spindle lock. 
     DISCLOSURE OF THE INVENTION 
     According to one aspect of the present invention there is provided a power tool comprising: 
     a housing, 
     a motor supported by the housing and including a motor shaft; 
     a spindle supported by the housing to turn about an axis, the spindle being selectively turned by the motor about the axis in first and second opposing directions; 
     a first locking member; 
     a second locking member movable between a locked position, in which the second locking member engages the first locking member to prevent rotation of the spindle, and an unlocked position; 
     a transmission for transmitting torque between the motor shaft and the spindle, the transmission including an inner rotor and an outer rotor that is mounted substantially about the inner rotor, the inner and outer rotors being mounted coaxially and for limited rotation relative to one another;
 
at least one pair of recesses, comprising first and second recesses provided on one of the inner and outer rotors,
 
at least one spring and at least one projection provided on the other of the inner and outer rotors, each projection being biased by the spring into a selected one of the first recess and the second recess, the springs being operable to delay movement of the second locking member from the unlocked position to the locked position when a force is applied to the spindle to cause the spindle to rotate relative to the motor shaft;
 
whereby, when the spindle is rotated in the first direction relative to the motor shaft, each projection is movable between a first position, which corresponds to the unlocked position of the second locking member and in which each projection is positioned in the first recess, and a second position, in which each projection is positioned in the second recess, movement of each projection from the first recess delaying movement of the second locking member from the unlocked position to the locked position; and
 
whereby, when the spindle is rotated in the second direction relative to the motor shaft, each projection is movable between the second position, which corresponds to the unlocked position of the second locking member and in which each projection is positioned in the second recess, and the first position, in which each projection is positioned in the first recess, movement of each projection from the second recess delaying movement of the second locking member from the unlocked position to the locked position.
 
     Preferably the first locking member comprises a wedge roller, brake shoe, or the like and the second locking member comprises a ramp surface, wedge, lever, or the like, which engages the first locking member, pressing it into contact with a rotating circumference to prevent rotation of the spindle. 
     Preferably the transmission further comprises a speed reduction gear transmission, driven by the motor shaft, and one or more output members of the transmission driving one of the inner and outer rotors. Preferably outer rotor is fixed to rotate with the one or more output members. Preferably the gear transmission comprises at least one planetary gearset, and the output members comprise axles supporting the planet gears, the axles being fixed to rotate with the outer rotor. 
     Preferably the first and second recesses are circumferentially spaced apart in an outer surface of the inner rotor and the projections extend from an inner surface of the outer rotor. This provides a compact design, since more space is available in the outer rotor for mounting the springs. 
     Preferably the projections are biased substantially in a radial direction. Preferably a radially elongated aperture is provided in the outer rotor for receiving each spring. Preferably the springs are helical. Optionally, the springs may have a spiral form. 
     Preferably the first and second recesses in the inner rotor are separated by a lobe having a form with reflective symmetry about a radial plane bisecting the lobe. 
     This invention provides a spindle lock for a power tool which is effective and efficient in operational use. It has been found that the torque between the inner and outer rotors can be more reliably maintained, and that there is correspondingly little variation in the delay provided by the springs mounted in this mechanism throughout the life of the tool. By providing the inner rotor generally within the outer rotor this advantage can be maintained without compromising the compactness of the tool. Moreover, a high degree of modularity is achieved, allowing a range of power tools to be provided using a number of common parts but using different springs for varying the torque applied between the inner and outer rotors during their “free” angle of rotation depending upon the torque capacity of the tool. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
         FIG. 1  is a schematic sectional view in a longitudinal plane through the drive axis of a power tool according to the invention; 
         FIG. 2  is an exploded pictorial view of the inner rotor and outer rotor assembly of the tool of  FIG. 1 ; 
         FIG. 3  is an end view of the drive rotor of the tool of  FIG. 1 ; 
         FIG. 4  is an end view of the inner rotor of the tool of  FIG. 1 ; 
         FIG. 5  is a composite of fragmentary sectional views along planes AA and BB of  FIG. 1 , and 
         FIG. 6  is a pictorial view of an inner rotor and outer rotor assembly according to a first alternative embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings,  FIG. 1  schematically illustrates a power tool having a spindle lock system  10  embodying the invention. As shown in  FIG. 1 , the power tool includes a housing  11  supporting a motor  12 . A spindle  13  is rotatably supported by the housing  11  and is reverseably driveable by the motor  12 . A tool holder or chuck (not shown) may be supported on the forward end of the spindle  13  for rotation with the spindle  13 . The power tool may be a drill (as illustrated) or another type of power tool, such as, for instance, a screwdriver, a grinder or a router. 
     The motor  12  includes an output shaft  12   a  defining a motor axis  14  and connected to a planetary speed reduction transmission  15  that includes a sun gear  16  connected, as by splines, to the output shaft  12   a ; a planet gear  17  supported by axles  50  fixed to a drive rotor or outer rotor  18  and engageable between the sun gear  16  and an internally toothed ring gear  19  fixed to the housing  11 . The outer rotor  18  thus provides the “planet carrier” that rotates with the motor shaft  12   a , while the axles  50  are output members transmitting torque to the outer rotor  18 . 
     The spindle lock system  10  is supported on the output side of the speed reduction transmission  15  and includes a driving torque structure  10 ′ for conveying torque from the outer rotor  18  to the spindle  13 , and locking structure  10 ″ for locking the spindle  13  and selectively preventing rotation of the spindle  13  relative to the housing  11  and relative to the outer rotor  18 . 
     The driving torque structure  10 ′ between the spindle  13  and the outer rotor  18  includes a male connector  19  formed on the end of the spindle  13  (as two parallel flats  20  on opposite sides of the spindle axis) and a female connector  22  formed on the outer rotor  18 . The connector  22  has sidewalls which are formed to provide a free angle  23  (of about 20 degrees in the illustrated construction) in which the spindle  13  and the outer rotor  18  are rotatable relative to one another to provide some rotational play between the spindle  13  and the outer rotor  18 . When the connectors  31  and  32  are engaged, there is a free rotational space in which the outer rotor  18  will not convey rotating force to the spindle  13  but in which the outer rotor  18  and the spindle  13  are rotatable relative to one another for the free angle  23 . In the illustrated construction, the shape of the connector  22  provides this free play in both rotational directions of the motor  12  and spindle  13 . 
     The locking structure  10 ″ generally includes a release member  24  fixed to the outer rotor  18 , one or more springs  25  (five are employed in the illustrated embodiment), a projection or ball  30  associated with each spring  25 , one or more locking members or wedge rollers  26 , a lock ring  27 , a rubber ring  28 , a fixing ring  29 , a detent rotor or inner rotor  31  and the spindle  13 . Except for the wedge rollers  26  and the spindle  13 , the other components of the locking structure  10 ″ are generally in the shape of a ring extending about the spindle axis. It will be understood that the drawings only schematically illustrates the major components of the locking structure  10 ″, and other less important parts are omitted for clarity. 
     The lock ring  27  and inner rotor  31  both include female connectors  32  complementary to the connector  19  on the spindle  13  so that both the lock ring  27  and inner rotor  31  are rotationally fast with the spindle  13 . On the outer circumference, the lock ring  27  includes dividing protrusions  34  which, in the illustrated construction, are equally spaced from each other by about 90 degrees. On each circumferential side of each protrusion  34 , inclined locking wedge surfaces  35   a  and  35   b  are defined to provide locking surfaces so that the spindle lock system  10  will lock the spindle  13  in the forward and reverse rotational directions. The wedge surfaces  35   a  and  35   b  are inclined toward the associated protrusion  34 . 
     In the illustrated construction, the locking members are wedge rollers  26  formed in the shape of a cylinder. A wedge roller  26  is provided for each locking wedge surface  35   a  and  35   b  of the lock ring  27 . The wedge rollers  26  are provided in four pairs, one for each protrusion  34 . One wedge roller  26  in each pair provides a locking member in the forward rotational direction of the spindle  13 , and the other wedge roller  26  in the pair provides a locking member in the reverse rotational direction of the spindle  13 . 
     The rubber ring  28  is supported in a groove in the fixing ring  29 , and engagement of the wedge rollers  26  with the rubber ring  28  causes rotation of the wedge rollers  26  due to the friction between the wedge rollers  26  and the rubber ring  28 . The fixing ring  29  defines an inner circumference  36  receiving the lock ring  27 . The inner circumference  36  of the fixing ring  29  and the outer circumference of the lock ring  27  (and/or of the spindle  13 ) face each other in a radial direction and are spaced a given radial distance such that a pair of wedge rollers  26  are placed between a pair of inclined locking wedge surfaces  35   a  and  35   b  of the lock ring  27  and the inner circumference  36 . 
     The inclined locking wedge surfaces  35   a  and  35   b  and the inner circumference  36  of the fixing ring  29  cooperate to wedge the wedge rollers  26  in place in a locked position which corresponds to a locked condition of the spindle lock system  10 , in which the spindle  13  is prevented from rotating relative to the housing  11  and relative to the motor  12  and outer rotor  18 . Space is provided between the inner circumference  36  of the fixing ring  29  and the outer circumference of the lock ring  27  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  13  is free to rotate relative to the housing  11 . 
     The releasing member  24  includes releasing protrusions  39  which are selectively engageable with the wedge rollers  26  to release or unlock the wedge rollers  26  from the locked position. The releasing protrusions  39  are, in the illustrated construction, equally separated by about 90 degrees to correspond with the relative position of the four pairs of wedge rollers  26 . Each releasing protrusion  34  is designed to release or unlock the associated wedge rollers  26  by engagement with the circumferential end part to force the wedge roller  26  in the direction of rotation of the releasing member  24  (and the outer rotor  18 ). The circumferential length of each releasing protrusion  34  is defined so that the releasing or unlocking function is accomplished within the free rotational angle  23  between the spindle  13  and the releasing member  24  and the outer rotor  18 . Preferably, the releasing or unlocking function is accomplished near the end of the free rotational angle  23 . 
     The detent rotor or inner rotor  31  is disposed generally within the drive rotor or outer rotor  18  with which it cooperates to provide a detent arrangement or controlling structure for controlling the resilient force of the springs  25  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  40  and  41  are defined on outer circumferential face of the inner rotor  31 . Five pairs of recesses  40 ,  41  are equally circumferentially spaced about the inner rotor  31 . The recesses  40 ,  41  of each pair are separated by a radially outwardly extending lobe  42  having a form with reflective symmetry about a radial plane  43  bisecting the lobe  42 . 
     The outer rotor  18  includes five equally angularly spaced slots  44  elongated radially. The through-extending axial opening through the outer rotor  18  has a stepped form with an outer section providing the female coupling  22  and adjacent inner section  60  having inner surface  45  of larger transverse dimension than the coupling  22 , and adapted to accept the inner rotor  31 . 
     A spring  25  is received in each aperture  44  and engages a ball  30  such that at least part of the balls  30  extends from the inner surface  45 . The springs  25  provides a resilient force to bias the projections, or balls  30  into engagement with a selected one of the recesses  40  and  41 . The slots  44  are open along an axial face and the slots  44  and inner section of the aperture  60  are closed by a retaining ring  48  secured, as by fasteners (not shown), to the outer rotor  18 . 
     The torque provided by the engagement between the balls  30  and recesses  40 ,  41  is such as to allow the projections to move from one recess (i.e., recess  41 ) to the other recess (i.e., recess  40 ), when the motor  12  is restarted. The resilient force the springs  25  apply to the balls  30  is set to allow the balls  30  to move from one recess (i.e., recess  40 ) to the other recess (i.e., recess  41 ) to control and buffer the rotational force of the spindle  13  when the motor  12  is stopped and to delay the engagement of the locking structure  10 ″. 
     In operation, when the outer rotor  18  is rotated in the direction of arrow X (in  FIG. 5 ) by operation of the motor  12 , the corresponding wedge roller  26   a  is pushed into a releasing or unlocked position of the inclined surface  35   a  of the lock ring  27  by the end of the releasing protrusion  34 . The other wedge roller  26   b  is kept in contact with the inner circumference  36  of the fixing ring  29 , and, by its frictional contact, the wedge roller  26   b  is pushed into the releasing position of the inclined surface  35   b . This releasing or unlocking function is accomplished within the free rotational angle  23  between the spindle  13  and the outer rotor  18  and the motor  12 . 
     After the locking structure  10 ″ is released or unlocked, the connecting part  32  of the outer rotor  18  and the connecting part  31  of the spindle  13  move into driving engagement so that the driving force of the outer rotor  18  (and motor  12 ) is transferred to the spindle  13  and the spindle  13  rotates with the outer rotor  18 . At this time, each ball  30  is positioned in one recess (i.e., recess  40 , the “run” position recess) of the inner rotor  31 , and the position of the releasing member  24  and the lock ring  27  is controlled by the resilient force of the springs  25  in a releasing or unlocked position at one end of the free angle  23 . 
     During driving operation of the motor  12 , the releasing protrusion  34  provides a force necessary to push the wedge roller  26   a  into the releasing or unlocked position and does not provide a large impact force on the wedge rollers  26   a . When the motor  12  is stopped (switched from the operating condition to the non-operating condition) rotation of the outer rotor  18  is stopped. Rotation of the spindle  13  is controlled and buffered by the resilient force of the springs  25  retaining the balls  30  in the selected recess (i.e., recess  40 ). During stopping, if the inertia of the spindle  13  (and the attached chuck and tool bit) is less than the resilient force of the springs  25 , rotation of the spindle  13  is stopped with the balls  30  being retained in the selected recess (i.e., recess  40 , the run position). In such a case, the resilient force of the springs  25  buffers and controls the inertia of the spindle  13  even when there is little or no relative rotation between the spindle  13  and the outer rotor  18  and the motor  12 . 
     When the inertia of the spindle  13  (and the attached chuck and tool bit) is greater than the resilient force of the springs  25 , the inertia overcomes the resilient force of the springs  25  and the friction between the balls  30  and the inclined ramp surface surface adjacent to the selected recess  40  so that the balls  30  move from the recess  40  and to the other recess  41  (the “lock” position recess). Movement of the balls  30  from recess  40  and to the recess  41  resists the rotational inertia of the spindle  13  and controls and buffers the rotational inertia of the spindle  13  so that the rotation of the spindle  13  will be dissipated before the locking structure  10 ″ engages. 
     Therefore, the rotational inertia of the spindle  13  (and the attached chuck and tool bit) is controlled and buffered by the engagement of the balls  30  in the respective recesses  40  and movement to the recesses  41  under the resilient spring force applied the respective springs  25 . The springs  25  controls the rotational force of the spindle  13  and delays the engagement of the wedge rollers  26  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  13  has stopped. Also, because the rotational force of the spindle  13  is controlled, there is no impact of the spindle lock and rebound through the free rotational angle  23  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  40  and  41  and the balls  30  and the resilient spring force provided by the springs  25 . 
     When the operator operates a chuck this tends to rotate the spindle  13  relative to the outer rotor  18  but, rotation of the spindle  13  is prevented because of the functioning of the locking structure  10 ″. The wedge rollers  26  will be wedged between the inner circumference  36  of the fixing ring  29  and the respective inclined locking wedge surfaces  35   a  and  35   b  of the lock ring  27  so that rotation of the spindle  13  in each rotational direction will be prevented. Because the spindle  13  is prevented from rotating, the chuck can be easily operated to remove and/or support a bit. 
     When the motor  12  is restarted, the end of the releasing protrusion  34  (in the selected rotational direction) moves one wedge roller  26   a  to a releasing position. The other wedge roller  26   b  engages the inner circumference  36  of the fixing ring  29  and is pushed into a releasing position. Once the wedge rollers  26  are released, the spindle  13  is free to rotate. The spindle  13  begins to rotate under the force of the motor  12  at the end of the free angle  23  of rotation between the spindle  13  and the outer rotor  18  and motor  12 . 
     When the spindle  13  is driven and the wedge rollers  26  rotate about their respective axes and revolve about the spindle  13 , the wedge rollers  26  are kept in contact with the rubber ring  28 , and this contact resistance causes the wedge rollers  26  to rotate while revolving. This rotation of the wedge rollers  26  and engagement with the supporting protrusions  38  of the supporting rings  23  on a trailing portion of the respective wedge rollers  26  maintains the respective axes of the wedge rollers  26  in an orientation in which the roller axes are substantially parallel to the axis of the spindle  13 . 
       FIG. 6  illustrates a first alternative embodiment of the inner and outer rotors  131 ,  118  of like construction and operation to the inner and outer rotors  31 ,  18  of  FIGS. 1-5 , but in which, the recesses  40 ,  41  are provided on the outer rotor  118  (instead of on the inner rotor) and the springs  25  and balls  30  are provided on the inner rotor  131  (instead of on the outer rotor). The recesses  40 ,  41  and associated lobes  42  are circumferentially spaced about the inner surface  45  of the recess  60  in which the inner rotor  131  is received. The inner rotor  131  includes five radial projections  70 , in each of which a slot is provided in which the spring  25  and ball  30  are disposed. 
     Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.