Abstract:
A vegetation pruning device includes a cutting element; a guide bar for supporting the cutting element, the guide bar having a guide bar plane, the guide bar being pivotable in the guide bar plane about a fixed axis; a motor having a motor shaft for rotatably driving the cutting element; a motor housing for receiving the motor; a guiding mechanism connected to the motor housing, the guiding mechanism having a longitudinal axis; a handle assembly operable to move linearly along the longitudinal axis; and a transmission device for connecting the handle assembly to the guide bar through, the transmission device converting a linearly movement of the handle assembly to a pivoting movement of the guide bar, the cutting element thereby approaching or withdrawing from a workpiece to be sawn.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the entry into the U.S. National Phase of PCT/CN2010/070675, filed Feb. 11, 2010, which claims priority to Chinese Patent Application Nos. CN200910008072.X, filed Feb. 20, 2009 and CN200910260820.3, filed Dec. 11, 2009, each of which is incorporated herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a power tool, more particularly to a vegetation pruning device. 
       BACKGROUND 
       [0003]    There are considerable array of tools available for the modern gardeners. For example, shears are used for pruning or cutting “light” vegetation such as grass or leaves or twigs etc. Hedge trimmers and chain saws are used for cutting “heavy” vegetation such as trees. 
         [0004]    A traditional chain saw comprises a cutting head. The cutting head comprises a flexible chain and a guide bar for supporting the flexible chain. The flexible chain is driven by a motor received in a motor housing and runs along the peripheral of the guide bar. A traditional chain saw further comprises a main handle positioned behind the cutting head, an assistant handle positioned between the cutting head and the main handle. During cutting, the cutting head is driven by the motor and the flexible chain runs along the peripheral of the guide bar, the guide bar does not move with respect to the motor housing. In operation, one hand of the operator grasps the main handle, and the other hand of the operator grasps the assistant handle, the operator should press the saw toward the cutting direction to ensure smoothly cutting. When the cutting direction is from up to down, operating of the traditional chain saw will be not so hard for the gravity of the saw. But if the cutting is from down to up or from left side to right side, operating of the traditional saw will be very hard and need great effort. 
         [0005]    U.S. Published Patent Application No. 2005/0022388A1 discloses a vegetation pruning device. The vegetation pruning device comprises a cutting head. The cutting head comprises a flexible chain and a guide bar for supporting the flexible chain. The flexible chain is driven by a motor and running around the guide bar. The vegetation pruning device further comprises a pair of pivotally coupled arms. The pivotally coupled arms rotate about a fixed axis. The cutting head is connected to one of the arm and can pivot together with the arm around the fixed axis relative to the other arm. Each arm is connected with a handle portion for the operator to grip. In use, the operator moves the handle portions close to each other, the arms will move close correspondingly, thereby the cutting work can be proceed. But this kind of vegetation pruning device makes that in some instance the operation is not so comfortable. For example, when you need to cut branch of high trees, it&#39;s hard to make such a cutting with this kind of vegetation pruning device. In other instance, such as cutting wood placed on the floor, the operator should bow, if the operating last long, it is very easy to feel exhaust. 
       SUMMARY 
       [0006]    It is an aspect of the present invention to provide a vegetation pruning device with improved operability. 
         [0007]    According to one aspect, a vegetation pruning device comprises: 
         [0008]    a cutting element; 
         [0009]    a guide bar for supporting the cutting element, the guide bar having a guide bar plane, the guide bar being pivotable in the guide bar plane about a fixed axis; 
         [0010]    a motor having a motor shaft for rotatably driving the cutting element; 
         [0011]    a motor housing for receiving the motor; 
         [0012]    a guiding mechanism connecting with the motor housing, the guiding mechanism having a longitudinal axis, 
         [0013]    a handle assembly operable to move linearly along the longitudinal axis, and 
         [0014]    a transmission device for connecting the handle assembly to the guide bar, the transmission device converting a linearly movement of the handle assembly to a pivoting movement of the guide bar, the cutting element thereby approaching or with drawing from a work piece to be sawn. 
         [0015]    Preferably, the handle assembly moves linearly, which makes the operator feel comfortable in any working instance. 
         [0016]    Advantageously, the transmission device may be configured as a crank mechanism. 
         [0017]    Advantageously, the crank mechanism may comprise a driving part, a connecting part and a driven part, the driving part is operable by the handle assembly, the driven part is fixedly attached to the guide bar, the connecting part is interposed between the driving part and the driven part, the connecting part is hinged to the driving part and the driven part respectively. 
         [0018]    Advantageously, the driven part may be configured as V-shaped, one side portion of the V-shaped driven part is hinged to the connecting part, another side portion of the V-shaped driven part is fixedly secured to the guide bar, a bottom portion of the V shaped driven part is pivotable about the fixed axis. 
         [0019]    Advantageously, the fixed axis may be configured as the motor shaft axis. 
         [0020]    Advantageously, the vegetation pruning device may comprise a driving device, the driving device is positioned between the motor shaft and the cutting element, the driving device includes a sprocket having a sprocket rotation axis, the sprocket is in meshing engagement with the cutting element so that the cutting element is running around the guide bar and the sprocket, the fixed axis is the sprocket rotation axis. 
         [0021]    Advantageously, the handle assembly may comprise a leading portion and a gripping portion. 
         [0022]    Advantageously, the leading portion may be configured as a longitudinal extension rod. 
         [0023]    Advantageously, the gripping portion may be configured as D-shaped. 
         [0024]    Advantageously, the guiding mechanism may be configured as a longitudinal extension tube having a longitudinal axis, the extension rod is movably received in the longitudinal extension tube, so that the extension rod can move linearly along the longitudinal axis of the longitudinal extension tube. 
         [0025]    Advantageously, a locking device may be associated with the longitudinal extension tube and the front portion. 
         [0026]    Advantageously, a control switch may be built into the D-shaped gripping portion. 
         [0027]    Advantageously, a safety switch may be symmetrically attached to both outer ends of the D-shaped gripping portion. 
         [0028]    Advantageously, the vegetation pruning device may comprise a U-shaped guard. 
         [0029]    Advantageously, the guard may comprise a first receiving room and a second receiving room, and the cutting head is completely insertable into the first receiving room. 
         [0030]    Advantageously, the cutting head may be at least partially insertable into the second receiving room. 
         [0031]    Advantageously, the U-shaped guard may comprise a first and a second supporting edge, which are connected to each other by a third supporting edge, and the first, second and third supporting edge, and the first, second and the third supporting edges define together a U-shaped supporting edge. 
         [0032]    Advantageously, the U-shaped guard may comprise a first end surface and a second end surface, the first end surface and the second end surface have a common plane, a supposed plane is perpendicular to the longitudinal axis and the fixed axis is positioned in the supposed plane, the longest distance between the points of the outermost layer of the cutting element and the supposed plane is less than or equal to the distance between the common plane of the first end surface and the second end surface and the supposed plane. 
         [0033]    Advantageously, the transmission device may be configured as a rack and pinion mechanism, the rack and pinion mechanism comprising a gear fixedly secured to the guide bar and a rack fixedly secured to the handle assembly, the gear is in meshing engagement with the rack so that a linearly movement of the rack can be changed to pivotable movement of the gear. 
         [0034]    Advantageously, the transmission device may be configured as a pulley mechanism, the pulley mechanism includes a pulley and a rope, the rope is mounted on the pulley, one end of the rope being fixed to the handle assembly, the other end of the rope being fixed to the motor housing, the pulley is fixedly coupled to the guide bar, so that a linearly movement of the handle assembly can be changed to a pivotable movement of the guide bar. 
         [0035]    According to another aspect, a vegetation pruning device comprises: 
         [0036]    a cutting element; 
         [0037]    a guide bar for supporting the cutting element; 
         [0038]    a motor for rotatably driving the cutting element; 
         [0039]    a handle assembly operable to move linearly; and 
         [0040]    a transmission device positioned between the handle assembly and the guide bar, 
         [0041]    the transmission device converting a linear movement of the handle assembly to a pivoting movement of the guide bar; 
         [0042]    the transmission device is associated with the motor and operable to drive the motor and guide bar to move together. 
         [0043]    Preferably, the guide bar rotates with the motor together, which makes the vegetation pruning device reduce the precision requirements of installation during manufacture, and which makes the operator more comfortable during operation. 
         [0044]    Advantageously, the vegetation pruning device may be configured as a chain saw. 
         [0045]    Advantageously, the transmission device may be configured as a synchronous belt drive mechanism. 
         [0046]    Advantageously, the handle assembly may comprise a gear rack, and the synchronous belt drive mechanism comprises a drive gear which meshes with the gear rack. 
         [0047]    Advantageously, the synchronous belt drive mechanism may comprise a follower bracket, and the guide bar is fixed secured to the follower bracket. 
         [0048]    Advantageously, the follower bracket may be fixed secured to the motor, thereby the motor rotates together with the follower bracket when the follower bracket rotates. 
         [0049]    Advantageously, the vegetation pruning device may further comprise a limiting mechanism for preventing the guide bar rotating to excess. 
         [0050]    Advantageously, the limiting mechanism may comprise a limited bracket with three waist-shaped grooves formed along the circumference at equal interval, and the motor comprises three projected columns formed at one end along the circumference at equal interval, the three projected columns extending along the motor shaft and passing through the three waist-shaped grooves respectively. 
         [0051]    Advantageously, the vegetation pruning device further may comprise a resilience mechanism. 
         [0052]    Advantageously, the vegetation pruning device further may comprise a main housing, the transmission device being configured as a synchronous belt drive mechanism, the synchronous belt drive mechanism comprising a follower bracket, the resilience mechanism comprising a pin and a spiral spring, one end of the spiral spring being connected with the follower bracket pivotally, the other end of the spiral spring is provided with a chute, the main body comprising a projected column accommodated in the chute, the spiral spring being mounted on the pin, one end of the spiral spring supported against the projected columns, and the other end of the spiral spring being pressed against the end of the pin so as to be pressed against the follower bracket. 
         [0053]    Advantageously, the transmission device may be configured as a plane multi-rod mechanism. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0054]      FIG. 1  is a perspective view of the pruning device in the form of a chain saw in accordance with the first embodiment. 
           [0055]      FIG. 2  shows schematically the internal mechanism of the chain saw according to  FIG. 1 . 
           [0056]      FIG. 3  shows principle diagram of the crank mechanism of the chain saw according to  FIG. 1 . 
           [0057]      FIG. 4  is a schematic view of the driving device of the chainsaw according to  FIG. 1 . 
           [0058]      FIG. 5  is a schematic view of the locking device of the chainsaw according to  FIG. 4 . 
           [0059]      FIG. 6A  is a schematic view of the chainsaw in unused status according to  FIG. 1 . 
           [0060]      FIG. 6B  is a schematic view of the chainsaw during operating status according to  FIG. 1 . 
           [0061]      FIG. 6C  is a schematic view of the chainsaw in an operating status near to end according to  FIG. 1 . 
           [0062]      FIG. 7  is a schematic view of the chainsaw when cutting a workpiece placed on the floor according to  FIG. 1 . 
           [0063]      FIG. 8  is a schematic view of the internal mechanism of the chainsaw in accordance with the second embodiment. 
           [0064]      FIG. 9  is a schematic view of the internal mechanism of the chainsaw in accordance with the third embodiment. 
           [0065]      FIG. 10  is a perspective view of the chain saw in accordance with the fourth embodiment. 
           [0066]      FIG. 11  is a schematic view of the chainsaw viewed from another visual angle according to  FIG. 10 . 
           [0067]      FIG. 12  is an exploded view of the chain saw when the motor housing is detached according to  FIG. 10 . 
           [0068]      FIG. 13  is an exploded view of the chain saw according to  FIG. 10 . 
           [0069]      FIG. 14  is a schematic view of the motor of the chainsaw according to  FIG. 10 . 
           [0070]      FIG. 15  is an exploded view of the main housing of the chain saw according to  FIG. 10 . 
           [0071]      FIG. 16  is a perspective view of the synchronous belt drive mechanism of the chainsaw according to  FIG. 10 . 
           [0072]      FIG. 17  is a perspective view of the limiting mechanism of the chainsaw according to  FIG. 10 . 
           [0073]      FIG. 18  is a perspective view of the chain saw in accordance with the fifth embodiment. 
       
    
    
     DETAILED DESCRIPTION 
     The First Embodiment 
       [0074]    Referring to  FIG. 1  and  FIG. 2 , a pruning device in the form of a chain saw  10  comprises a cutting head  12  for working on a workpiece. The cutting head  12  comprises a guide bar  14  and a cutting element mounted on the guide bar  14 . In present embodiment, the cutting element is a flexible chain  16 . The flexible chain  16  is mounted on the periphery of the guide bar  14 . The flexible chain  16  runs along the periphery of the guide bar  14 . The guide bar  14  has a guide bar plane. 
         [0075]    The chain saw  10  comprises a motor  18  for driving the cutting head  12  so that the flexible chain  16  runs around the guide bar  14 . The motor  18  has a motor shaft  20 . The motor shaft  20  has a motor shaft axis X 1 . The motor shaft  20  rotates about the motor shaft axis X 1  thereby to drive the flexible chain  16  running around the guide bar  14 . 
         [0076]    The motor  18  is received in a motor housing  24 . In present embodiment the motor housing  24  is building up from two half shells. However the motor housing is not limited to such a specific form, it can be other usual forms in the present field. 
         [0077]    An U-shaped guard  26  is connected to one end of the motor housing  24 . One side of the U-shaped guard  26  is an upper guard  28 . The other side of the U-shaped guard  26  is a lower guard  30 . The bottom portion of the U-shaped guard  26  is a coupling portion  31 . The U-shaped guard  26  connects with the motor housing  24  by the coupling portion  31 . The upper guard  28  has a first receiving room  32 . The cutting head  12  is totally housed in the first receiving room when the chain saw  10  is not in use. The lower guard  30  has a second receiving room  34 . The cutting head  12  can be partially received in the second receiving room  34  of the lower guard  30  when the cutting operation is near to end. The upper guard  28  has a pair of side walls  36 . The guide bar  14  is positioned between the pair of side walls  36 . A plurality of openings  38  are formed on the side walls  36 . The opening  38  is used for observing the movement of the cutting head  12 , so that the operator know clearly the current position of the cutting head  12 . The side walls  36  has a first supporting edge  40  formed on the side near the lower guard  30 . The lower guard  30  has a pair of side walls  42 . The cutting head  12  is operable to receive between the pair of side walls  42 . The side walls  42  has a second supporting edge  44  formed on the side near the upper guard  28 . The coupling portion  31  has a third supporting edge  46  formed thereon. The third supporting edge  46  is used for connecting the first supporting edge  40  and the second supporting edge  44 . The first supporting edge  40 , the second supporting edge  44  and the third supporting edge  46  together defines a substantially U-shaped supporting edge  47 . In use the U-shaped supporting edge  47  is used to support the workpiece. 
         [0078]    The upper guard  28  has a first end surface  48 . The lower guard  30  has a second end surface  50 . In the present embodiment, the first end surface  48  and the second end surface  50  have a common plane. However, the first end surface  48  and the second end surface  50  can be in different plane respectively. For example, the first end surface  48  and the second end surface  50  are two paralleling planes. The first end surface  48  or the second end surface  50  may be curved surface, such as cone-shaped surface. The first end surface  48  is perpendicular to the side walls  36 . The second end surface is perpendicular to the side walls  42 . The first end surface  48  and/or the second end surface  50  might not perpendicular to the side walls  36  and/or the side walls  40 . The first receiving room  32  is defined by the first end surface  48  and the side walls  36 . The second receiving room  34  is defined by the second end surface  50  and the side walls  42 . 
         [0079]    A guiding mechanism is connected to the other end of the motor housing  24 . In the present embodiment, the guiding mechanism is served by a longitudinal extension tube  52 . The longitudinal extension tube  52  has a longitudinal axis X 2 . The longitudinal extension tube  52  has a receiving cavity  54 . 
         [0080]    The chain saw  10  further comprises a handle assembly  56 . The handle assembly  56  comprises leading portion  58  and gripping portion  60 . The leading portion  58  is a longitudinal extension rod. The leading portion  58  is received in the receiving cavity  54  of the longitudinal extension tube  52 . The gripping portion  60  looks like a substantially D-shape. The D-shaped gripping portion  60  has a grasping side  62  and a connecting side  64 . A control switch  66  is building in the inner part of the grasping side  62 . The control switch  66  is electrically connected to the motor  18  to control the start and stop of the motor  18 . A pair of safety switches  68  is symmetrically attached to both ends of the grasping side  62 , such a construction makes that operation is becoming convenient no matter what hand is used. The connecting side  64  couples the leading portion  58 . 
         [0081]    A transmission device is positioned between the handle assembly  56  and the cutting head  12 . In the present embodiment, the transmission device is provided to connect the handle assembly  56  and the guide bar  14  directly. The transmission device is served to change the linearly movement of the handle assembly  56  to the pivoting movement of the guide bar  14 . In the present embodiment, the transmission device is a crank mechanism  70 . The crank mechanism  70  includes driving part  72 , connecting part  74  and driven part  76 . The driving part  72  is served by the leading portion  58  of the handle assembly  56 . The leading portion  58  moves linearly along the longitudinal axis X 2  of the longitudinal extension tube  52  when the operator pushes the gripping portion  60  toward the cutting head  12 . The driven part  76  is fixedly attached to the guide bar  14 . The connecting part  74  is interposed between the driving part  72  and the driven part  76 . The connecting part  74  is hinged to the driving part  72  and the driven part  76  respectively. The driven part  76  looks like a substantially V-shape. One side portion  78  of the V-shaped driven part  76  is hinged to the connecting part  74 . The other side portion  80  of the V-shaped driven part  76  is fixedly secured to the guide bar  14 . The bottom portion  81  of the V-shaped driven part  76  is pivotably mounted on the motor shaft  20 , thereby the driven part  76  can rotate around the motor shaft axis X 1  of the motor shaft  20 . Because the driven part  76  is fixedly secured to the guide bar  14 , when the driven part  76  rotates around the motor shaft axis X 1 , the guide bar  14  rotates together therewith about the motor shaft axis X 1  in the guide bar plane. 
         [0082]      FIG. 3  discloses the principle diagram of the crank mechanism  70 . The driving part  72  moves linearly. The driven part  76  pivots from the first position (solid line for reference) to the second position (broken line for reference) when the driving part  72  moves from the first position (solid line for reference) to the second position (broken line for reference). The moving direction of the driving part  72  is represented by arrow A 1 . The moving direction of the driven part  76  is represented by arrow A 2 . 
         [0083]    Referring to  FIG. 4 , the chain saw  10  comprises a driving device  82  positioned between the motor  18  and the cutting head  12 . The driving device  82  includes pinion  84  formed on the motor shaft  20 . The pinion  84  can rotate together with the motor shaft  20  about the motor shaft axis X 1 . The driving device  82  further comprises a gear  86  in meshing engagement with the pinion  84 . The gear  86  is mounted to a middle shaft  88 . The middle shaft  88  has middle shaft axis X 3 . A sprocket  90  is mounted on the middle shaft  88  also. The sprocket  90  has sprocket rotation axis. In the present embodiment, the sprocket rotation axis is middle shaft axis X 3 . The sprocket  90  and the gear  86  together rotate about the middle shaft axis X 3 . The sprocket  90  is in meshing engagement with the flexible chain  16  to drive the flexible chain  16  running around the guide bar  14 . 
         [0084]    In use, switch on the chain saw  10 , the motor shaft  20  will rotate. The pinion  84  rotates together with the motor shaft  20 . The pinion  84  drives the gear  86  to rotate. The gear  86  and the sprocket  90  are mounted coaxially, so the sprocket  90  will rotate together with the gear  86 . The sprocket  90  then drives the flexible chain  16  to run around the guide bar  14 . The operator grasps the gripping portion  60  of the handle assembly  56  and pushes the handle assembly  56  toward the cutting head  12 , the leading portion  58  will move linearly along the longitudinal axis X 2  of the longitudinal extension tube  52 , then the driven part  76  can pivot around the motor shaft  20 , thereby drives the guide bar  14  pivoting about the motor shaft  20  in the guide bar plane. In the present embodiment, the cutting operation is achieved by pushing the handle assembly  56  toward the cutting head  12  to pivot the guide bar  14 . It should be noted that ordinary skilled person in the present field can change the placement of the crank mechanism, so that cutting operation can be achieved by pulling the handle assembly  56  away from the cutting head  12 . 
         [0085]    Further referring to  FIG. 5 , a locking device  92  is attached to the longitudinal extension tube  52  and the leading portion  58  of the handle assembly  56 . The locking device  92  comprises a pair of push buttons  94  oppositely attached thereon and a locking block  96  interposed between the push buttons  94 . The locking block  96  comprises a first locking end  98  and a second locking end  100 . The leading portion  58  comprises a first aperture  102  and a second aperture  104  for receiving the first locking end  98  and the second locking end  100  respectively. The locking block  96  has a pivoting axis  106 . The locking block  96  can pivot about the pivoting axis  106  by press either of the push button  94 , thereby the first locking end  98  and the second locking end  100  comes out from the first aperture  102  and the second aperture  104  respectively, thereby the leading portion  58  of the handle assembly  56  can move relative to the longitudinal extension tube  52 , or vice versa. 
         [0086]      FIG. 6A ,  FIG. 6B  and  FIG. 6C  illustrate the chain saw  10  in different operating process.  FIG. 6A  shows the chain saw  10  in unused status. When the chain saw  10  is not in use, the cutting head  12  is totally received inside the upper guard  28 . Referring to  FIG. 6B , push the handle assembly  56  along the direction of arrow A, the cutting head  12  will pivot along the direction represented by arrow B and start cutting the workpiece when coming out therefrom gradually. Referring to  FIG. 6C , keep pushing the handle assembly  56  along the direction represented by arrow A, the cutting head  12  will pivot along the direction represented by arrow B continuously and enter into the lower guard  30  so to end the cutting operation. 
         [0087]    Further referring to  FIG. 6B  and  FIG. 7 , the cutting head  12  comprises a proximal end near the motor shaft  20  and a distal end away from the motor shaft  20 . The outermost layer of the distal end is the periphery of the flexible chain. The pivoting axis of the guide bar  14  is the motor shaft axis X 1 . Here a supposed plane M 1  is perpendicular to the longitudinal axis X 2  and the motor shaft axis X 1  is located therein. The longest distance between the points in the outermost layer of the distal end of the cutting head and the supposed plane M 1  is L 1 . If the first end surface  48  of the upper guard  28  and the second end surface  50  of the lower guard  30  are positioned in a common plane, the distance between the common plane and the supposed plane M 1  is L 2 . If the first end surface  48  of the upper guard  28  and the second end surface  50  of the lower guard  30  are positioned in different plane, the longest distance between points in the first end surface  48  of the upper guard  28  or the second end surface  50  of the lower guard  30  and the supposed plane M 1  is L 2 . 
         [0088]    In the present embodiment, distance L 1  is shorter than distance L 2 . The advantage of such a design is: when the workpiece is placed on the floor (see  FIG. 7 ), the chain saw is holded by the operator in a direction that the longitudinal axis of the chain saw  10  perpendicular to the floor. The first end surface  48  and the second end surface  50  contacts with the floor to support the chain saw  10  thereon, thereby the distal end of the cutting head  12  will not touch the floor so as to protect the cutting head  12 . In some instance, when the workpiece is placed on the grassland or sandlot, distance L 1  can be equal to or a little longer than the distance L 2 , under this circumstance, the outermost layer of the cutting head  12  may touch the soft grassland or sandlot, however the soft grassland or sandlot will not make damage to the cutting head  12 . 
       The Second Embodiment 
       [0089]      FIG. 8  illustrates a second embodiment similar to the first embodiment, yet in which the crank mechanism  70  is replaced by a rack and pinion mechanism  70   a . The rack and pinion mechanism  70   a  comprises a rack  72   a  fixedly secured to the handle assembly  56  and a gear  74   a  fixedly secured to the guide bar  14 . Pushing or pulling the handle assembly  56  will cause the gear  74   a  to rotate so to initiate a pivoting movement of the guide bar  14 . 
       The Third Embodiment 
       [0090]      FIG. 9  illustrates a third embodiment similar to the first embodiment, yet in which the crank mechanism  70  is replaced by a pulley mechanism  70   b . The pulley mechanism  70   b  includes a pulley  72   b  and a rope  74   b . The rope  74   b  is mounted on the pulley  72   b . One end of the rope  74   b  is fixed to the handle assembly  56 . The other end of the rope  74   b  is fixed to the motor housing  24 . The pulley  72   b  is fixedly coupled to the guide bar  14  through a connecting rod  76   b . In use, the operator pulls the handle assembly  56  in the direction represented by arrow C, which will cause the pulley  72   b  to rotate and the connecting rod  76   b  will rotate together therewith. The pivoting of the guide bar  14  will be initiated by the rotating of the connecting rod  76   b.    
       The Fourth Embodiment 
       [0091]    Referring to  FIG. 10  and  FIG. 11 , a chain saw  10 ′ comprising a working head  122  for processing a workpiece, the working head  122  comprising a guide bar  124  and a cutting element mounted on the guide bar  124 . The cutting element is a flexible chain  126  which is mounted on the periphery of the guide bar  124  and can rotate around the guide bar  124 . The plane where the guide bar  124  exists is a guide bar plane. 
         [0092]    Further referring to  FIG. 12 ,  FIG. 13  and  FIG. 14 , the chain saw  10 ′ also comprises a motor  128  for driving the working head  122  and enabling the flexible chain  126  to rotate around the guide bar  124 . The motor  128  has a motor output shaft  130  which has a motor output shaft axis X 1 ′ and rotates around the motor output shaft axis X 1 ′ so as to drive the flexible chain  126  to rotate around the guide bar  124 . The motor  128  is accommodated in a motor housing  132 . 
         [0093]    Further referring to  FIG. 15 , the chain saw  10 ′ comprises a main housing  134  consisting of two semi-housings, a first semi-housing  134   a  and a second semi-housing  134   b  respectively, which can be detachably connected through screws. In the other embodiments of the invention, the connection modes of the first semi-housing  134   a  and the second semi-housing  134   b  may be others means to those people who skilled in the field, for example, integral formed, or Snap-fit etc. The motor housing  132  can be detachably connected to the first semi-housing  134   a . In one embodiment of the invention, the motor housing  132  is connected to the first semi-housing  134   a  through screws. 
         [0094]    The chain saw  10 ′ comprises a housing cover  135 , and an access hole (not shown in figure) is formed on the second semi-housing  134   b  to guarantee that a user exchange the flexible chain  126  conveniently. In the embodiment, the housing cover  135  is fixed to the second semi-housing  134   b  pivotally. In other embodiments of the invention, the housing cover  135  is connected to the second semi-housing  134   b  by others means which the people who skilled in the field known. When the flexible chain  126  is not required to be exchanged, the housing cover  135  covers the access hole. When the flexible chain  126  is required to be exchanged, the user can open or dismantle the housing cover  135  from the second semi-housing  134   b  through tools such as a wrench. 
         [0095]    The chain saw  10 ′ comprises a handle assembly  136  (as shown in  FIG. 10 ,  FIG. 11  or  FIG. 12 ) for being held by an operator during use. As shown in  FIG. 15 , the first semi-housing  134   a  comprises a first working head accommodating end  138   a , a first handle accommodating end  140   a , and a first connection part  142   a  for connecting the first working head accommodating end  138   a  and the first handle accommodating end  140   a . The second semi-housing  134   b  comprises a second working head accommodating end  138   b , a second handle accommodating end  140   b , and a second connection part  142   b  for connecting the second working head accommodating end  138   b  and the second handle accommodating end  140   b.    
         [0096]    Both the first working head accommodating end  138   a  and second working head accommodating end  138   b  are approximately U-shaped. The first working head accommodating end  138   a  has a first U-shaped opening  143   a . The second working head accommodating end  138   b  has a second U-shaped opening  143   b.    
         [0097]    The first working head accommodating end  138   a  and the second working head accommodating end  138   b  together form a U-shaped protective hood  138  (as shown in  FIG. 10 ) which is used for accommodating the working head  122 . 
         [0098]    The first working head accommodating end  138   a  comprises a first upper lateral wall  144   a  and a first lower lateral wall  146   a . The first U-shaped opening  143   a  is defined between the first upper lateral wall  144   a  and the first lower lateral wall  146   a . The second working head accommodating end  138   b  comprises a second upper lateral wall  144   b  and a second lower lateral wall  146   b . A second U-shaped opening  143   b  is defined between the second upper lateral wall  144   b  and the second lower lateral wall  146   b.    
         [0099]    A first accommodating space  148  (as shown in  FIG. 10 ) is formed between the first upper lateral wall  144   a  and the second upper lateral wall  144   b . A second accommodating space  150  (as shown in  FIG. 10 ) is formed between the first lower lateral wall  144   b  and the second lower lateral wall  146   b . The first accommodating space  148  and the second accommodating space  150  are used for accommodating the working head  122 . The first upper lateral wall  144   a  and the second upper lateral wall  144   b  are provided with several openings  152  respectively, so that the operator can get a clear view of the current position of the working head through the openings  152 . 
         [0100]    The first working head accommodating end  138   a  has a first U-shaped inside edge  154   a  which is circularly arranged on the inner side of the first working head accommodating head  138   a , namely on one side, close to the first U-shaped opening  143   a , of the first working head accommodating head  138   a , and a first U-shaped jaw  156   a  (as shown in  FIG. 11 ) is detachably arranged on the first U-shaped inner edge  154   a . The U-shaped jaw  156   a  comprises a plurality of teeth  158   a  arranged on the inner side of the first U-shaped jaw  156   a . The first U-shaped jaw  156   a  is made of steel. The first U-shaped jaw  156   a  is connected to the first U-shaped inner edge  154   a  through a rivet. 
         [0101]    The second working head accommodating end  138   b  has a second U-shaped inside edge  154   b  which is circularly arranged on the inner side of the second working head accommodating head  138   b , namely on one side, close to the second U-shaped opening  143   b , of the second working head accommodating head  138   b , and a second U-shaped jaw  156   b  (as shown in  FIG. 10 ) is detachably arranged on the second U-shaped inner edge  154   b . The second U-shaped jaw  156   b  comprises a plurality of teeth  158   b  arranged on the inner side of the second U-shaped jaw  156   b . The second U-shaped jaw  156   b  is made of steel. The second U-shaped jaw  156   b  is connected to the second U-shaped inner edge  154   b  through rivets. 
         [0102]    The first U-shaped inside edge  154   a  and the second U-shaped inside edge  154   b  together form a U-shaped inside edge  154  of the U-shaped protective hood  138 . The first U-shaped jaw  156   a  and the second U-shaped jaw  156   b  together form a U-shaped jaw  156  of the U-shaped protective hood  138 . The U-shaped jaw  156  of the U-shaped protective hood  138  is detachably connected to the U-shaped inside edge  154  of the U-shaped protective hood  138 . The abovementioned U-shaped jaw  156  can be used for supporting against a workpiece to be cut as a supporting wall. Teeth  158   a  and  158   b  are circularly arranged on the inner side of the U-shaped jaw  156 . The aim of setting the teeth  158   a  and  158   b  that, when slim twigs are cuted, the U-shaped jaw  156  with the teeth can reliably support the twigs and prevent the twigs from springing out. 
         [0103]    Referring to  FIG. 11  and  FIG. 12 , the motor housing  132  is connected to a first connection part  142   a  of the first semi-housing  134   a  through screws. Both the first handle accommodating end  140   a  of the first semi-housing  134   a  and the second handle accommodating end  140   b  of the second semi-housing  134   b  extend longitudinally, and connected through screws. The first handle accommodating end  140   a  of the first semi-housing  134   a  and the second handle accommodating end  140   b  of the second semi-housing  134   b  together form a handle accommodating end  140  of the main housing  134 . 
         [0104]    The handle accommodating end  140  has a handle accommodating chamber  159  formed between the first handle accommodating end  140   a  and the second handle accommodating end  140   b  for accommodating a handle assembly  136 . The handle accommodating chamber  159  has a longitudinal extension axis X 2 ′, and the handle assembly  136  is accommodated in the handle accommodating chamber  159  and can be operated to move linearly along the longitudinal extension axis X 2 ′. 
         [0105]    Further referring to  FIG. 10  and  FIG. 11 , the handle component  136  comprises a guide rod part  160  and a holding part  162 , the guide rod part  160  is a slim rod and accommodated in the handle accommodating chamber  159 , while the holding part  162  is approximately D-shaped. One side of the D-shaped holding part  162  is a straight holding edge  164 . The other side of the D-shaped holding part  162  is an arc-shaped connection edge  166 . The holding part  162  is connected with the guide rod part  160  through the connection edge  166 . A control switch  168  electrically connected with a motor  128  for controlling the start and stop of the motor  128  is arranged on the inner side of the holding edge  164 . 
         [0106]    The guide rod part  160  is accommodated in the handle accommodating chamber  159  and can be operated to move linearly along the longitudinal extension axis X 2 ′ of the handle accommodating chamber  159 . 
         [0107]    A transmission device is arranged between the handle component  136  and the working head  122 . In the embodiment, the transmission device connects the handle component  136  and the guide bar  124  and converts the linear motion of the handle component  136  into the pivot motion of the guide bar  124 . In the embodiment, the transmission device is configured as a synchronous belt drive mechanism  172 . 
         [0108]    Referring to  FIG. 16 , one side, away from the holding part  162 , of the guide rod part  160  is a drive part  174  with an approximate U-shaped cross section, a gear rack  176  is arranged on the bottom face of the U-shaped drive part  174 , and a chute  178  is arranged on each of two sides of the U-shaped drive part  174 . 
         [0109]    The synchronous belt drive mechanism  172  comprises a drive gear  180  and a second drive gear  182 . The first drive gear  180  and the second drive gear  182  are coaxially arranged and both fixedly supported on a first support shaft  184 , and such connection makes the three rotate synchronously. Two ends of the first support shaft  184  pass through the chutes  178  respectively. Two accommodating holes (not shown) are formed on the first semi-housing  134   a  and the second semi-housing  134   b  respectively, and the two ends of the first support shaft  184  are accommodated in the two accommodating holes respectively. The two ends of the first support shaft  184  can relatively move along the chutes  178  with respect to the chutes  178  and can rotate in the two accommodating holes. 
         [0110]    The first drive gear  180  is meshing engagement with the gear rack  176 . When the guide rod part  60  of the handle component  36  moves linearly along the longitudinal extension axis X 2 ′ of the handle accommodating chamber  159 , the gear rack  176  drives the first drive gear  180  to rotate, so the second drive gear  182  follows the first drive gear  180  to rotate. 
         [0111]    The synchronous belt drive mechanism  172  further comprises a synchronous belt  186 , a third drive gear  188 , a fourth drive gear  190  and a second support shaft  192 . 
         [0112]    The third drive gear  188  and the fourth drive gear  190  are coaxially arranged and both fixedly supported on the second support shaft  192 , and such connection makes the three rotate synchronously. Two accommodating holes (not shown) are formed on the first semi-housing  134   a  and the second semi-housing  134   b  respectively, and the two ends of the second support shaft  192  are accommodated in the two accommodating holes respectively and can rotate therein. 
         [0113]    The synchronous belt  186  is mounted on the second drive gear  182  and the third drive gear  188 , so when the second drive gear  182  rotates it drive the third drive gear  188  to rotate through the synchronous belt  186 , and then the fourth drive gear  190  rotates together with the third drive gear  188 . 
         [0114]    The synchronous belt drive mechanism  172  further comprises a follower bracket  194  provided with a fan-shaped gear  196 . The fan-shaped gear  196  is meshing engagement with the fourth drive gear  190 , so when the fourth drive gear  190  rotates, the follower bracket  194  and the fan-shaped gear  196  rotate together with the fourth drive gear  190 . In one embodiment of the invention, the follower bracket  194  is mounted on the motor output shaft  130  and can rotate around the output shaft  130  of the motor. 
         [0115]    The guide bar  124  is fixedly connected with the follower bracket  194 , so when the follower bracket  194  rotates around the motor output shaft  130 , the guide bar  124  also rotates around the motor output shaft  130 . 
         [0116]    Referring to  FIG. 13  and  FIG. 17 , the chain saw  10 ′ comprises a limiting mechanism for limiting the guide bar  124  rotating in excess so as to prevent the U-shaped protection hood  138  from damaging due to the rotation of the guide bar  124 . The limited mechanism comprises a limited bracket  196  with a round cross section. Three waist-shaped grooves  198  are formed on the limited frame  196  along the circumference at equal interval, each of which extends along the circumference. 
         [0117]    Referring to  FIG. 14 , three projected columns  200 , extending from the upper edge of the end part of the motor  128  along the direction of the motor output shaft  130 , are arranged at an equal interval along the circumference direction. An accommodating hole  202  is formed on each projected column  200 . The three projected columns  200  pass through the three waist-shaped grooves  198  respectively and can rotate along the circumference direction therein. 
         [0118]    Referring to  FIG. 16 , a mounting hole  204  is formed on the middle position of the follower bracket  194 , the follower bracket  194  is sleeved on the motor output shaft  130  through the mounting hole  204 . Three accommodating holes  206  are formed on the follower bracket  194  at an equal interval in the circumference direction and respectively aligned with the three accommodating holes  202  formed on the three project columns  200 , such that a bolt can pass through the accommodating hole  206  and the accommodating hole  202  to fixedly connect the follower bracket  194  and the projected columns  200 . The follower bracket  194  is fixedly connected with the guide bar  124 , so the guide bar  124  is fixedly connected with the project columns  200 , furthermore, the follower bracket  194  is fixedly connected to the motor  128 , and such connection mode makes the follower bracket  194  rotate and drive the motor  128  to rotate together. 
         [0119]    One end of each waist groove  198  is provided with a first stop face  208 , while the other end is provided with a second stop face  210 , the projected columns  200  are operated to move in the waist-shaped groove  198  and matched with the first stop face  208  and the second stop face  210  respectively. When the projected columns  200  are matched with the first stop face  208 , the working head  122  is accommodated in the first accommodating space  148 . When the guide bar  124  rotates to the top of the U-shaped protection hood  138  and the working head  122  keeps a certain distance away from the top of the U-shaped protection hood  138 , so the working head  122  does not contact the top of the U-shaped protection hood  138 . When the projected columns  200  are matched with the second stop face  210 , the working head  122  is accommodated in the second accommodating space  150 . When the guide bar  124  rotates to the bottom of the U-shaped protection hood  138  and the working head  122  keeps a certain distance away from the bottom of the U-shaped protection hood  138 , so the working head  122  does not contact the bottom of the U-shaped protection hood  138 . 
         [0120]    A resilience mechanism is arranged between the second semi-housing  134   b  and the follower bracket  194 . The resilience mechanism comprises a pin  212  and a spiral spring  214 , one end of the pin  212  is pivoted with the follower bracket  194 , the other end  212  is provided with a chute  216 , and the second semi-housing  134   b  is provided with the projected columns (not shown in the figure) which are accommodated in the chute. The spiral spring  214  is mounted on the pin, one end of the spiral spring is supported against the projected columns, and the other end of the spiral spring  214  is pressed against the end of the pin  212  so as to be pressed against the follower bracket  194 . The resilience mechanism is arranged to ensure that, whenever after the end of cutting, the working head  122  can automatically spring back to the initial position, which means the working head  122  springs back into the first accommodating space  148 . The working head  122  is completely accommodated in the U-shaped protection hood  138 , which guarantees the safety of operation. 
         [0121]    The chain saw  10 ′ comprises a drive mechanism positioned between the motor  128  and the working head  122  and used for transferring the power of the motor  128  to the working head  122 . The drive mechanism comprises a chain wheel  220  disposed on the motor output shaft  130  and can, together with the motor output shaft  130  rotate around the axis X 1 ′ of the motor output shaft  130 . The chain wheel  220  is meshing engagement with the flexible chain  126  to drive the flexible chain  126  to rotate around the guide bar  124 . 
         [0122]    The motor  128  can be started by manually pressing the control switch  168  during working, and then the motor output shaft  130  starts to rotate, the chain wheel  220  rotates together with the motor output shaft  130 , and the chain wheel  220  rotates to drive the flexible chain  126  to rotate around the guide bar  124 . Meanwhile, if the operator holds the holding part  162  of the handle component  136  and pushes the handle component  136  towards the working head  122 , the guide rod part  160  linearly moves along the longitudinal extension axis X 2 ′ of the handle accommodating chamber  159 , under the action of the synchronous belt drive mechanism  172 , the guide bar  124  pivots around the axis X 1 ′ of the motor output shaft in the support plate plane, and thus cutting starts. The guide bar  124  is fixedly connected with the motor  128 , so the pivot of the guide bar  124  drives the motor  128  to rotate together. In the embodiment, the handle component  136  is pushed towards the working head  122 , so the guide bar  124  pivots to cut. 
       The Fifth Embodiment 
       [0123]      FIG. 18  shows another embodiment, which is different from the fourth embodiment in that: the transmission device is configured as a plane multi-rod mechanism  230  comprising a connection rod  232 . The connection rod  232  is positioned between the guide rod part  160  and the follower bracket  194  and hinged with the two respectively. The connection rod  232  comprises a first connection rod  234 , a second connection rod  236  and a third connection rod  238 . When the operator pushes the holding  162  towards the working head  122 , the guide rod part  160  linearly moves along the longitudinal extension axis X 2 ′ of the handle accommodating chamber  159 . The follower bracket  194  is fixedly connected with the guide bar  124 , and the first connection rod  234 , the second connection rod  236  and the third connection rod  238  are positioned between the guide rod part  160  and the follower bracket  194 . One end of the first connection rod  234  is hinged with the guide rod part  160  of the handle component  136 . The other end of the first connection rod  234  is hinged with one end of the second connection rod  236 , and the other end of the second connection rod  236  can be relatively pivoted with the first semi-housing  134   a . One end of the third connection rod  238  is hinged with the middle part of the second connection rod  236 , while the other end of the third connection rod  238  is hinged with the follower bracket  194 . The embodiment ensures that, when the handle component  136  is pushed towards the working head  122 , the guide bar  124  pivots to cut.