Patent Document

FIELD OF THE INVENTION 
   The present invention relates to a mode selection mechanism for a power tool, and relates particularly, but not exclusively, to a mode selection mechanism for preventing simultaneous actuation of a scrolling mode of a jigsaw (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 of a jigsaw (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 a mode selection mechanism. 
   BACKGROUND OF THE INVENTION 
   EP0158325 discloses a jigsaw having (i) a scrolling mode in which an output shaft and jigsaw blade can rotate about a longitudinal axis of the output shaft to enable cutting of smaller radii of curvature or more intricate types of cut than conventional jigsaws in which the jigsaw blade only faces forwards, and (ii) an orbital mode in which the output shaft oscillates about a pivot in a fore and aft direction to assist the cutting action of the jigsaw blade. 
   In jigsaws having a scrolling mode and an orbital mode, it is desirable to prevent simultaneous actuation of the scrolling and orbital modes, since the jigsaw is difficult to operate when in the orbital mode when the jigsaw blade is not oriented forwards relative to the jigsaw housing. In the jigsaw of EP0158325, this is carried out by means of a mode selection mechanism in which a mode selector is provided with a pinion and a cam surface, such that in an orbital mode, the pinion moves a rack into engagement with a scroller knob to prevent rotation of the scroller knob relative to the housing, while in the scrolling mode, the cam surface prevents pivoting movement of the output shaft of the jigsaw about its pendulum axis. However, this known arrangement suffers from the drawback that the rack and pinion mechanism is of complicated construction and relatively difficult to assemble, which significantly increases the cost of production of a jigsaw incorporating this mechanism. 
   Another jigsaw having scrolling and orbital modes is disclosed in DEU8702727.5. In this jigsaw, a mode selection knob moves a carriage between an upper position in the orbital mode, in which rotation of an output shaft of the jigsaw about its longitudinal axis is prevented, and a lower position in the scrolling mode, in which pivoting of the output shaft about an axis transverse to its longitudinal axis is prevented. However, this jigsaw suffers from the disadvantage that the carriage cannot be used to simultaneously disable the scrolling and orbital modes, as a result of which a further actuator mechanism is required. This in turn has the disadvantage of increasing the cost of production of the jigsaw and making the jigsaw less easy to use. 
   Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art. 
   BRIEF SUMMARY OF THE INVENTION 
   According to an aspect of the present invention, there is provided a mode selection apparatus 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 mode selection apparatus comprising: 
   at least one locking member moveable between a respective first position in which an output shaft of the tool is pivotable about its longitudinal axis, a respective second position in which the output shaft is prevented from pivoting about its longitudinal axis and is prevented from engaging a drive mechanism to prevent the output shaft from pivoting about a pivot axis transverse to said longitudinal axis, and a respective third position in which the output shaft is prevented from pivoting about its longitudinal axis and engages said drive mechanism to cause the output shaft to pivot about the pivot axis transverse to said longitudinal axis, wherein said locking member has at least one respective first protrusion and/or recess; and 
   at least one mode selection member for engaging a respective said locking member for moving the locking member between first, second and third positions thereof and having at least one second protrusion and/or recess for engaging a respective said first recess and/or protrusion on said locking member; 
   wherein at least one said protrusion and/or recess of a said mode selection member is adapted to remain in engagement with the corresponding said recess and/or protrusion of a said locking member during movement of said locking member between said first, second and third positions thereof. 
   By providing at least one protrusion and/or recess of a mode selection member which is adapted to remain in engagement with the corresponding recess and/or protrusion of a locking member during movement of the locking member between its first, second and third positions, this provides the advantage of making the mode selection apparatus of more simple construction and easier to assemble than a mechanism employing a rack and pinion, which significantly reduces the cost of production of a tool incorporating the apparatus. In addition, by providing at least one mode selection member for moving a respective locking member between the first, second and third positions thereof, this provides the advantage of enabling three modes of a tool incorporating the mode selection apparatus, for example scrolling mode, orbital mode and conventional mode of a jigsaw, to be selected by means of a single actuator, which in turn makes the tool more convenient to operate. 
   At least one said locking member may be adapted to engage a first actuator member on said tool housing in said first and second positions to prevent rotation of said first actuator member relative to the tool housing. 
   At least one said locking member may be adapted to engage at least one respective slot and/or protrusion on the first actuator member. 
   At least one said mode selection member may have at least one respective cam surface for causing the output shaft to move out of engagement with the drive mechanism to prevent the output shaft from pivoting about the pivot axis transverse to said longitudinal axis. 
   At least said one cam surface may be a groove. 
   At least one said cam surface may be a protrusion. 
   At least one said mode selection member may be adapted to rotate relative to the tool housing. 
   The apparatus may further comprise at least one first actuator member for enabling rotation of the output shaft about said longitudinal axis. 
   The apparatus may further comprise at least one second actuator member for actuating at least one said mode selection member for moving at least one said locking member between first, second and third positions thereof. 
   According to another aspect of the present invention, there is provided a power tool having a tool housing, a motor arranged in the tool housing, 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, and a mode selection apparatus as defined above. 
   The power tool may be a jigsaw. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a cross-sectional elevation view of a jigsaw embodying the present invention; 
       FIG. 2  is a perspective view of a blade support assembly, jigsaw blade and scrolling knob of the jigsaw of  FIG. 1 ; 
       FIG. 3  ( a ) is a perspective view of an upper bearing of the blade support assembly of  FIG. 2 ; 
       FIG. 3(   b ) is a front view of the upper bearing of  FIG. 3(   a ); 
       FIG. 3(   c ) is a top view of the upper bearing of  FIG. 3(   a ); 
       FIG. 3(   d ) is a side view of the upper bearing of  FIG. 3(   a ); 
       FIG. 3(   e ) is a bottom view of the upper bearing of  FIG. 3(   a ); 
       FIG. 3(   f ) is a side cross sectional view of the upper bearing of  FIG. 3(   a ); 
       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 ; 
       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; 
       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; 
       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; 
       FIG. 6(   a ) is a front view of a scotch yoke, output shaft and blade clamp of the blade support assembly of  FIG. 2 ; 
       FIG. 6(   b ) is a perspective view of the scotch yoke, output shaft and blade clamp of  FIG. 6(   a ); 
       FIG. 6(   c ) is a top view of the scotch yoke of  FIGS. 6(   a ) and  6 ( b ); 
       FIG. 7  is a perspective view of the blade support assembly of  FIG. 2 ; 
       FIG. 8  is a top view of the blade support assembly of  FIG. 7 ; 
       FIG. 9  is a rear view of the blade support assembly of  FIG. 7 ; 
       FIG. 10  is a side cross sectional view along the line A-A in  FIG. 8 ; 
       FIG. 11  is a view along the line B-B in  FIG. 10 ; 
       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 
       FIG. 13  is a view corresponding to  FIG. 12  when the blade is cutting a workpiece. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   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. 
   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 . 
   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. 
   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 groove  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 cam portion  46  of the scroll selector  48  is a protrusion  47  that rotates with the scroll selector  48  in the embodiment of  FIG. 1  and a groove  88  formed in the outer periphery  85  of the a post  89  of the scroll selector  48  in the embodiment of  FIGS. 5(   a ) to  5 ( c ). 
   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 slots  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 end  82  of locking arm  76  is not received within the groove  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  63  ( FIG. 1 ) 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. 
   As the scroll selector  48  is rotated anticlockwise about axis  90  to the position shown in  FIG. 5(   b ), engagement of tooth  86  with rounded groove  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 the groove  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 . 
   As the scroll selector  48  is further rotated anticlockwise about axis  90  to the position shown in  FIG. 5(   c ), the upper end  78  of locking arm  76  is received further in one of the slots  80 , but the lower end  82  of locking arm  76  is now received in the groove  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 the rounded 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. 
   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. 
   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. 
   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 . 
   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 . 
   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 . 
   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 . 
   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