Patent Document

FIELD OF THE INVENTION  
       [0001]     The present invention relates to an output shaft assembly for a power tool, and relates particularly, but not exclusively, to an output shaft assembly for a jigsaw having a scrolling mode (i.e. in which an output shaft supporting a jigsaw blade can rotate about its longitudinal axis relative to the jigsaw housing) and an orbital mode (i.e. in which the output shaft is pivotable relative to the housing about an axis transverse to its longitudinal axis, so that an oscillating motion is superimposed on the axial reciprocating motion of the jigsaw blade). The invention also relates to a power tool incorporating such an output shaft assembly.  
       BACKGROUND OF THE INVENTION  
       [0002]     A jigsaw having scrolling and orbital modes is disclosed in EP 0158325. The jigsaw has an output shaft of generally circular cross section in order to enable the output shaft to pivot about its longitudinal axis in the scrolling mode of the jigsaw relative to a scotch yoke mechanism driving the output shaft in a reciprocating motion relative to the jigsaw housing.  
         [0003]     However, in order to enable the orientation of the output shaft of such jigsaws relative to the jigsaw housing, and relative to any jigsaw blade mounted to the output shaft, to be controlled, the output shaft is provided with cross pins at its upper and lower ends which cooperate with slots in a scroller knob and a blade support assembly respectively, in order to prevent rotation of the output shaft relative to the scroller knob and blade support. This causes the disadvantage that the slots with which the cross pins cooperate must be as long as the distance of travel of the cross pins in an axial direction in order to ensure permanent engagement of the cross pins with the slot, as a result of which the overall height of the jigsaw is large, which obstructs viewing of the jigsaw blade during cutting thereof, and the width of the forward part of the jigsaw around the output shaft is also large as a result of this.  
         [0004]     The overall length and diameter of the parts of the jigsaw around the output shaft can be made smaller by having an output shaft of generally flat cross-section which fits into a correspondingly shaped slot in a scroller knob at its upper end, and to the lower end of which a jigsaw blade is clamped. However, it has not been possible to provide a scroller mode of such jigsaws because of the difficulty in making the output shaft rotatable relative to the jigsaw housing.  
         [0005]     Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     According to an aspect of the present invention, there is provided an output shaft assembly for a power tool having a tool housing, a motor arranged in the tool housing, and an output shaft adapted to be driven in a reciprocating motion relative to the tool housing by means of the motor and to support a working member of the tool for reciprocating motion of the working member relative to the tool housing, the output shaft assembly comprising: 
        an output shaft having first and second portions adjacent respective ends of said shaft and having non-circular cross-section in a direction transverse to a longitudinal axis of said shaft, and at least one third portion between said first and second portions and having at least partially substantially circular external cross-section in use in a direction transverse to the longitudinal axis of said shaft to allow said shaft to pivot about said longitudinal axis relative to a drive mechanism for driving said shaft in a reciprocating motion relative to the tool housing.        
 
         [0008]     By providing an output shaft having first and second portions adjacent respective ends of the shaft and having non-circular cross-section in a direction transverse to a longitudinal axis of the shaft, and at least one third portion between the first and second portions and having at least partially substantially circular external cross-section section in a direction transverse to the longitudinal axis of the shaft to allow the shaft to pivot about the longitudinal axis relative to a drive mechanism for driving the shaft in a reciprocating motion relative to the tool housing, this provides the advantage of combining the benefits of a substantially flat output shaft enabling a more compact construction of the tool in the vicinity of the output shaft, and rotation of the output shaft relative to a drive mechanism, for example to provide a scroller mode when the tool is a jigsaw.  
         [0009]     At least one said third portion may be formed from a plurality of insert members mounted to the output shaft in use.  
         [0010]     This provides the advantage of simplifying construction of the output shaft, which in turn reduces the cost of manufacture of a tool incorporating the output shaft.  
         [0011]     The output shaft may have substantially uniform cross-section in a direction transverse to said longitudinal axis prior to mounting of said inserts to said output shaft.  
         [0012]     At least one said insert member may have substantially D-shaped cross-section.  
         [0013]     The assembly may further comprise at least one drive member pivotably mounted to at least one said third portion in use for engaging a drive mechanism for driving said shaft in a reciprocating motion relative to the tool housing.  
         [0014]     According to another aspect of the present invention, there is provided a power tool comprising a tool housing, a motor arranged in the tool housing, and an output shaft assembly as defined above having an output shaft adapted to be driven in a reciprocating motion relative to the tool housing by means of the motor and to support a working member of the tool for reciprocating motion of the working member relative to the tool housing.  
         [0015]     The power tool is preferably a jigsaw. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     Preferred embodiments of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:  
         [0017]      FIG. 1  is a cross-sectional elevation view of a jigsaw embodying the present invention;  
         [0018]      FIG. 2  is a perspective view of a blade support assembly, jigsaw blade and scrolling knob of the jigsaw of  FIG. 1 ;  
         [0019]      FIG. 3  ( a ) is a perspective view of an upper bearing of the blade support assembly of  FIG. 2 ;  
         [0020]      FIG. 3 ( b ) is a front view of the upper bearing of  FIG. 3 ( a );  
         [0021]      FIG. 3 ( c ) is a top view of the upper bearing of  FIG. 3 ( a );  
         [0022]      FIG. 3 ( d ) is a side view of the upper bearing of  FIG. 3 ( a );  
         [0023]      FIG. 3 ( e ) is a bottom view of the upper bearing of  FIG. 3 ( a );  
         [0024]      FIG. 3 ( f ) is a side cross sectional view of the upper bearing of  FIG. 3 ( a );  
         [0025]      FIG. 4  is a side view of the blade support assembly, jigsaw blade and scrolling knob of  FIG. 2 , together with a drive mechanism of the jigsaw of  FIG. 1 , but having an alternative embodiment of scroll selector to the arrangement shown in  FIG. 1 ;  
         [0026]      FIG. 5 ( a ) is a perspective view of the scroller knob and scroller locking mechanism of  FIG. 4  in a scrolling mode of the jigsaw;  
         [0027]      FIG. 5 ( b ) is a perspective view, corresponding to  FIG. 5 ( a ) of the scroller knob and scroller locking mechanism in a conventional mode of the jigsaw;  
         [0028]      FIG. 5 ( c ) is a perspective view, corresponding to  FIG. 5 ( a ) of the scroller knob and scroller locking mechanism in an orbital mode of the jigsaw;  
         [0029]      FIG. 6 ( a ) is a front view of a scotch yoke, output shaft and blade clamp of the blade support assembly of  FIG. 2 ;  
         [0030]      FIG. 6 ( b ) is a perspective view of the scotch yoke, output shaft and blade clamp of  FIG. 6 ( a );  
         [0031]      FIG. 6 ( c ) is a top view of the scotch yoke of FIGS.  6 ( a ) and  6 ( b );  
         [0032]      FIG. 7  is a perspective view of the blade support assembly of  FIG. 2 ;  
         [0033]      FIG. 8  is a top view of the blade support assembly of  FIG. 7 ;  
         [0034]      FIG. 9  is a rear view of the blade support assembly of  FIG. 7 ;  
         [0035]      FIG. 10  is a side cross sectional view along the line A-A in  FIG. 8 ;  
         [0036]      FIG. 11  is a view along the line B-B in  FIG. 10 ;  
         [0037]      FIG. 12  is an enlarged view of the lower part of the blade support assembly of  FIG. 10  when the blade is not cutting a workpiece; and  
         [0038]      FIG. 13  is a view corresponding to  FIG. 12  when the blade is cutting a workpiece. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]     Referring to  FIG. 1 , a jigsaw  2  has a housing  4  comprising two clam shell halves  6  (only one of which is shown in  FIG. 1 ) defining a handle  8  having a trigger switch  10  for operating a motor  12  supplied with electrical power via a cable  14 . A shoe  16  for resting on a workpiece (not shown) is located at a lower part of the housing  4 , and a jigsaw blade  18  ( FIG. 2 ) is attached to the lower end of an output shaft  20  by means of a blade clamp mechanism  22 . The operation of the blade clamp mechanism  22  is not relevant to an understanding of the present invention and will therefore not be described in greater detail herein. The orientation of the shoe  16  is adjustable relative to the housing  4  to enable bevel cutting, and can be fixed by means of a clamping screw  24  operated by a locking mechanism  26 , which is also not relevant to an understanding of the present invention and will therefore not be described in greater detail.  
         [0040]     The motor  12  drives a shaft  28  which carries a fan  30 . When the fan  30  rotates, air is expelled via duct  32  and may be used to blow sawdust away from the vicinity of blade  18 , and draws air through inlets  34  in housing  4  to cool motor  12 . The shaft  28  carries a pinion  36  which meshes with a drive gear  38  mounted about axis  40 , the gear  38  carrying a cam surface  42  on its front face. A cam follower  44  is selectively engageable with cam surface  42  by means of cam portion  46  of scroll selector  48  to operate an orbital mode of the jigsaw in a manner which will be described in greater detail below. The gear  38  also carries an eccentric pin  50  which slidably fits in a slot  52  of scotch yoke mechanism  54  mounted to output shaft  20 .  
         [0041]     Referring now to  FIG. 2 , a scroller knob  56  is rotatably mounted to the housing  4  for adjusting the orientation of the blade  18  relative to the housing  4 . The scroller knob  56  has a collar portion  58  having a cruciform bore  60  therein, the purpose of which is described in greater detail below. A blade support assembly  62  has a support housing  64  having trunnions  66  which are received in corresponding recesses (not shown) in housing  4  to enable the assembly  62  to pivot about axis X-X relative to the housing  4  in the orbital mode of the jigsaw. An upper bearing  68  ( FIG. 3 ) has a partially spherical portion  70  which is rotatable about axis Y-Y relative to support housing  64 , and has a slot  72  therethrough for receiving the output shaft  20  such that the output shaft  20  can slide in the direction of axis Y-Y relative to the upper bearing  68 , but is prevented from moving relative to the bearing  68  in a direction transverse to the axis Y-Y. The upper bearing  68  also has a pair of legs  74  which are received in cruciform bore  60  of scroller knob  56  such that the bearing  68  (and therefore the output shaft  20 ) rotates with the scroller knob  56  about axis Y-Y, but limited pivoting movement of the bearing  68  about axis X-X relative to the scroller knob  56  is permitted.  
         [0042]     A mechanism for selecting between the scrolling, orbital and conventional modes of the jigsaw is shown in detail with reference to  FIGS. 4 and 5 . A locking arm  76  is slidably mounted to the housing  4  and is moveable between a lower position, as shown in  FIG. 5 ( a ) in which the scroller knob  56  can rotate relative to the housing  4 , and two upper positions shown in FIGS.  5 ( b ) and  5 ( c ) in which an upper end  78  of the locking arm  76  is received in one or more slots  80  in the underside of scroller knob  56  to prevent rotation of the scroller knob  56  about axis Y-Y relative to the housing  4 . The scroll selector  48  is rotatably mounted to the housing  4  and can be rotated by means of a mode selector knob (not shown) on the housing  4 , and a lower end  82  of locking arm  76  has a rounded slot  84  which receives a rounded tooth  86  provided on scroll selector  48  such that rotation of scroll selector  48  relative to the housing  4  causes movement of the locking arm  76  parallel to the axis Y-Y. The scroll selector  48  also carries a cam surface, which is a protrusion  46  in the embodiment of  FIG. 1  and a groove  88  in the embodiment of FIGS.  5 ( a ) to  5 ( c ).  
         [0043]     Referring now to FIGS.  5 ( a ) to  5 ( c ), in the position shown in  FIG. 5 ( a ), the rotational position of scroll selector  48  about axis  90  relative to the housing  4  is such that the upper end  78  of locking arm  76  is not receiving in any of the grooves  80  in scroller knob  56 , as a result of which the scroller knob  56  (and therefore also the output shaft  20  and jigsaw blade  18 ) can rotate about axis Y-Y relative to the housing  4  to permit scrolling motion of the blade  18 . At the same time, it is desirable to prevent orbital motion of the blade  18  when the jigsaw is in the scroller mode, since it is difficult to operate the jigsaw in the orbital mode when the orientation of the blade  18  relative to the housing  4  is not forwards. This is achieved in the position shown in  FIG. 5 ( a ) because the lower part  82  of locking arm  76  is not received within recess  88 , as a result of which the locking arm  76  is urged forwards relative to the scroll selector  48 . This in turn abuts lower portion  92  ( FIG. 2 ) of support housing  64 , which causes the support assembly  62  to pivot forwards against the action of a spring (not shown) about axis X-X so that cam follower  44  is held out of engagement with cam face  42  on gear  38 . As a result, pendulum motion cannot be imparted to the support assembly  62  as the gear  38  rotates.  
         [0044]     As the scroll selector  48  is rotated anticlockwise about axis  90  to the position shown in  FIG. 5 ( b ), engagement of tooth  86  with slot  84  causes the locking arm  76  to move upwards so that its upper end  78  is received in a slot  80  in scrolling knob  56  to prevent rotation of the scrolling knob  56  relative to the housing  4 . At the same time, the lower end  82  of the locking arm  76  is still not received in recess  88 , as a result of which the cam follower  44  is still held out of engagement with the cam surface  42  on gear  38 , so pendulum action cannot be imparted to the support assembly  62 .  
         [0045]     As the scroll selector  48  is further rotates anticlockwise about axis  90  to the position shown in  FIG. 5 ( c ), the upper end  78  of locking arm  76  is received further in groove  80 , but the lower end  82  of locking arm  76  is now received in recess  88  on scroll selector  48 . As a result, the support assembly  62  and locking arm  76  can pivot under the action of the spring (not shown) to bring the cam follower  44  into engagement with cam surface  42  on gear  38 , so that pendulum action is imparted to the support assembly  62  as the gear  38  is rotated by motor  12 . It can therefore be seen that the scrolling mode is not permitted when the orbital mode is active, and vice versa. By operating the locking arm  76  by means of the engagement of a tooth  86  in a groove  84  (as opposed to cooperating rack and pinion), this provides the advantage of significantly simplifying manufacture and assembly of the scroll locking mechanism, which in turn reduces the cost of production of the jigsaw.  
         [0046]     Referring now to FIGS.  6 ( a ) to  6 ( c ), the output shaft  20  is of rectangular cross section along most of its length. This provides the advantage that the ends of the shaft  20  can be non-rotatably mounted to adjacent parts without the need to provide cross pins (which would be necessary in the case of a shaft of circular cross section) through the shaft which would need to fit into slots at least as deep as the distance of travel of the cross pins during reciprocating motion of the shaft  20 . As a result, the parts of the jigsaw at the ends of the shaft  20  can be made of significantly more compact construction than is the case with a shaft of circular cross section.  
         [0047]     In order to enable rotation of the shaft  20  relative to the scotch yoke  54  in scrolling mode of the jigsaw, a pair of generally D-shaped inserts  94  are mounted on opposite sides of the shaft  20  to provide that part of the shaft with a partially circular external cross section, and the scotch yoke  54  is rotatably mounted to the shaft  20  by means of circular apertures  96  in upper and lower flanges  98  of the scotch yoke  54 . The scotch yoke  54  is then fixed to the shaft  20  by means of pins  100  through D-shaped inserts  94  and shaft  20  so that the scotch yoke  54  cannot move axially relative to the shaft  20 , but can pivot about relative to the shaft so that the slot  52  of scotch yoke  54  continues to face eccentric pin  50  ( FIG. 1 ) regardless of the orientation of the blade  18  relative to the housing  4 . This enables the blade  18  to be driven in a reciprocating manner when the jigsaw is in the scroller mode.  
         [0048]     The support assembly  62  of  FIG. 2  is shown in detail in FIGS.  7  to  13 . A lower bearing  102  is rotatably mounted about the longitudinal axis of the output shaft  20  to the support housing  64  and has a slot, similar to the slot  72  in upper bearing  68 , for slidably receiving the shaft  20  so that the shaft can execute reciprocating axial movement relative to the bearings  68 ,  102 , but is prevented from moving in a direction transverse to its longitudinal axis. The lower bearing  102  has four protruding legs  104  at its lower end, so that a cruciform slot ( FIG. 11 ) is defined between the legs  104  for receiving the shaft  20  and for cooperating with ribs  120  provided on a control bearing  106  such that the control bearing  106  rotates with the lower bearing  102  and output shaft  20  as the output shaft rotates about its longitudinal axis. The control bearing  106  is rotatably mounted to support housing  64  by means of engagement of a flange  116  on support housing  64  with a groove in control bearing  106 .  
         [0049]     The control bearing  106  has a support arm  108  which carries a blade support roller  110  at a distal end thereof. The blade support roller  110  has a groove  112  ( FIG. 1 ) for receiving the rear face of jigsaw blade  18 . Because the control bearing  106  is rotatably mounted to support housing  64 , the blade support roller  110  remains in contact with the jigsaw blade  18  in the scrolling, orbital and conventional modes of the jigsaw. The lower bearing  102 , control bearing  106  and support housing  64  are so dimensioned that limited pivoting of control bearing  106  relative to lower bearing  102  is possible about an axis transverse to the longitudinal axis of the shaft  20 , and limited movement of the control bearing  106  relative to the support housing  64  is possible, with movement due to clearance  122  between control bearing  106  and support housing  64  being taken up by an elastomeric seal  118 , which also prevents leakage of lubricant from the interior of the support assembly  62 .  
         [0050]     Referring now in detail to  FIGS. 12 and 13 , when the jigsaw is used to cut a workpiece (not shown), the reaction force from the workpiece acting on the blade  18  tends to cause the blade  18  to pivot clockwise relative to the shaft  20  form the position shown in  FIG. 12  to that shown in  FIG. 13 . As a result, a turning moment is applied via blade support roller  110  to the support arm  108  in the direction of arrow C shown in  FIG. 13 . This turning moment is opposed by an opposite turning moment applied to the control bearing  106  by the support housing  64  as the clearance  122  is reduced from the arrangement shown in  FIG. 12   c  to that shown in  FIG. 13 .  
         [0051]     However, as a result if the limited pivoting movement permitted between control bearing  106  and lower bearing  102 , the turning moment applied by the support arm  108  to the support housing  64  is not transferred to the lower bearing  102 , and is therefore not transferred to the shaft  20 . The therefore provides the advantage that frictional forces between the lower bearing  102  and shaft  20  are not increased as a result if reaction force F ( FIG. 13 ) acting on blade support roller  110 .  
         [0052]     It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Technology Category: b