Abstract:
In an angle-grinder with a rotating handle and a latch for fixing the handle in two different rotational positions, an interlock mechanism is provided for greater security against unwanted rotation of the handle when the tool is being used. The interlock mechanism is moved to a locking position by depressing the trigger to start the motor, and thus provides a safety lock backing up the latch, in case the latch is accidentally released during use. In its unlocking position the interlock mechanism may prevent actuation of the trigger when the handle is not properly aligned in one of its operating positions.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a hand-held power tool, particularly an angle grinder. In particular it relates to such a hand-held power tool which has a housing for receiving an electric motor, a tool head and a handle arranged on opposite ends of the housing, the handle being rotatable relative to the housing, and a locking device for fixing the housing and handle in at least two different positions. 
       BACKGROUND OF THE INVENTION 
       [0002]    Hand-held power tools, particularly angle grinders, typically have an on/off switch for the electric motor which is actuated via a trigger. The trigger is situated at the underside of the handle and is actuated by at least one finger when grasping the handle and held in an actuated position while the machine is in use. The design of the handle and trigger is such that it can best be used in one individual working position relative to the user. However an angle grinder, for instance, is regularly rotated about 90 degrees in use between two different orientations: a first with the disc roughly horizontal (e.g. for grinding or sanding) and a second where the disc is roughly upright (e.g. for cutting). To accommodate these two operating orientations in an ergonomically satisfactory manner a rotatable handle may be provided. Such a handle may rotate generally about its longitudinal axis, relative to the housing and tool head fixed to the housing and can be fixed in defined rotational positions by a latching arrangement. 
         [0003]    In a hand-held power tool of this type the handle housing may be provided with a collar which receives a complementary neck of the motor housing. The latching arrangement has at least two locking recesses in the motor housing so as to be offset relative to one another by a rotational angle. A locking member may be pivotally connected to the handle and spring-biased to engage in the locking recesses, and manually releasable before turning the handle between operation positions. It will be understood that the security of this latching arrangement is very important for safe tool operation, and one way in which security has been improved has been to use a clamping device, together with the locking member, which clamps the handle to the tool housing in the two operating positions. However, clamping devices are relatively costly to produce so there remains an unmet need to improve the security of the handle in power tools of this type, without substantially increasing manufacturing costs. It is an object of the present invention to address this need or more generally to provide an improved hand-held power tool. 
       DISCLOSURE OF THE INVENTION 
       [0004]    According to one aspect of the present invention there is provided a hand-held power tool, comprising: 
         [0005]    a housing holding a motor; 
         [0006]    a tool head arranged at one end of the motor housing and having a projecting drive spindle for a tool; 
         [0007]    a handle attached to another end of the motor housing and having a trigger moveable from an extended position in which the motor is switched off and a retracted position in which the motor is switched on, the handle being rotatable relative to the motor housing around a longitudinal axis of the motor housing; 
         [0008]    a manually actuated latch for fixing the handle in at least two different rotational positions, and 
         [0009]    an interlock mechanism having a locking and an unlocking position, the interlock mechanism cooperating with the trigger such that with the trigger in the extended position the interlock mechanism is in the unlocking position and with the trigger in the retracted position the interlock mechanism is in the locking position for fixing the handle in the at least two different rotational positions. 
         [0010]    Preferably the motor housing includes first, second, third and fourth recesses and the interlock mechanism includes an interlock lever pivoted by movement of the trigger from the extended to the retracted position, and wherein at the two different rotational positions the latch is engaged with one of the first and second recesses, while the interlock lever is engaged with one of the third and fourth recesses. Alternatively, it will be understood that the interlock mechanism may act to prevent movement of the latch from freeing the handle to rotate whenever the trigger is pressed. 
         [0011]    It will be understood that the interlock mechanism may include a number of types of known components or assemblies, for instance, the interlock mechanism may include an interlock slider which reciprocates along a predefined path between the locking and unlocking positions, instead of a pivoting lever. In place of a single member, multiple cooperating elements may be employed. 
         [0012]    Preferably the trigger is elongated in the direction of a longitudinal axis of the handle, the handle is provided with one of a collar and a complementary neck received therein, the motor housing having the other of the collar and complementary neck, one end of the trigger is coupled to the handle by a pivot proximate an outer end of the handle, and the other end of the trigger is disposed near the collar, the outer end of the trigger abutting the interlock lever in the locking position. 
         [0013]    Preferably when the handle is not at one of the two different rotational positions the locking lever is held in its unlocking position and acts upon the trigger, preventing the trigger moving to its retracted position to switch on the motor. 
         [0014]    Preferably interlock lever includes a boss through which a fulcrum shaft passes to mount the interlock lever to the handle, and the interlock lever includes first and second arms inclined obliquely to one another, the first arm abutting the trigger and the second arm engaging the third and fourth recesses. 
         [0015]    Preferably the interlock mechanism further includes a torsion spring for urging the interlock lever to rotate towards its unlocking position, the torsion spring having a helical portion disposed generally coaxially with the fulcrum shaft. 
         [0016]    This invention provides a hand-held power tool device with a locking rotatable handle which is effective and efficient in operational use, and which may be economically constructed due to its overall simple design. The interlock mechanism provides greater security for the rotating connection between the handle and the motor housing, preventing any accidental actuation of the latch from freeing the handle to rotate whenever the trigger is pressed and the tool is in use. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
           [0018]      FIG. 1  is a side view of a hand-held electric angle grinder according to the invention; 
           [0019]      FIG. 2  is an enlarged view of the handle with parts of the motor housing of the angle grinder of  FIG. 1 , partially in section; 
           [0020]      FIG. 3  shows a side view of the interlock lever of  FIG. 2 , and 
           [0021]      FIG. 4  shows a section along line AA in  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    In one preferred embodiment an electric hand-held power tool according to the invention is provided in the form of an angle grinder as shown in  FIG. 1 , which generally includes a motor housing  12 , a tool head  14  which is arranged at one end of the motor housing  12  and has a projecting drive spindle  15  for a grinding disc  16 , and a handle  10  which is arranged at the other end of the motor housing  12  and is constructed so as to be rotatable relative to the motor housing  12  around the longitudinal axis of the latter over a predetermined angle. The handle  10  includes a grip  17  which is grasped by the hand when working with the angle grinder and a trigger  18  which actuates an on/off switch for an electric drive motor  19  accommodated in the motor housing  12 . The tool head  14  is fixed with the motor housing  12 , while the handle  10  which is rotatable relative to the motor housing  12  and can be fixed in two different angular positions by a latch  20  mounted to the handle  10 . In the first position of the motor housing  12  and handle  10  shown in  FIG. 1  the angle grinder is used for grinding or sanding. In this relative position, the grinding disc  16  is roughly parallel to the work surface. By rotating the motor housing  12  by 90 degrees relative to the handle  10 , the angle grinder can be moved out of this first position into a second position for cutting work. In this second position of the angle grinder the handle  10  is maintained in the position shown in  FIG. 1  and the motor housing  12 , including the tool head  14 , is rotated by  90 .degree. so that the grinding disc  16  assumes the position shown in dashed lines in  FIG. 1  in which it is aligned approximately at a right angle to the work surface. 
         [0023]    Referring to  FIGS. 2 to 4 , the handle  10  may be formed from two elongate moulded polymeric shells (one of which is shown removed in  FIG. 1 ), while  FIG. 1  shows the motor housing  12  in longitudinal section. To provide the rotary joint between the engaging ends of the handle  10  and motor housing  12 , a collar  21  on the handle  10  receives a complementary neck  22  on the motor housing  12 , the collar  21  and neck  22  may have slidingly engaged circumferential rib and groove pairs which cooperate to provide a rotary bearing. 
         [0024]    The latch  20  and an interlock mechanism  22  may be mounted on generally opposing sides of the handle  10 , near diametrically opposing sides of the collar  21 . The latch  20  includes a latching member  23  pivotally mounted to the handle  10  and urged outwardly from the handle  10  by a spring  24 . A finger  26  formed on one end of the latching member  23  projects into the neck  22  of the motor housing  12  and has a shape complementary to first and second recesses  25   a,    25   b  formed in the neck  22  90 degrees apart. The latch  20  may be manually be depressed from the latched position shown in  FIG. 2  to disengage the finger  26  from the recess  25   a  and it serves to fix the handle  10  in two different rotational positions defined by the recesses  25   a,    25   b.    
         [0025]    The trigger  18  is recessed within a concavity  13  formed in the handle  10  and is of a known type, being elongated in the direction of a longitudinal axis of the handle  10 . One end of the trigger  18  is coupled to the handle  10  by a transverse pivot  28  proximate an outer end of the handle  10 , and the other end of the trigger  18  is disposed near the collar  21 , the trigger  18  having an outer end  29  opposite the pivot  28 . The trigger  18  pivots between the extended position shown in which the motor  19  is switched off and a retracted position (shown in dashed outline in Fig,  2 ) in which the trigger  18  actuates a switch  30  to switch in the motor  19  when the tool is in use. 
         [0026]    The interlock mechanism  22  includes an interlock lever  30  with a boss  31  through which a transverse fulcrum shaft  32  passes to mount the interlock lever  30  to the handle  10 . First and second arms  33 ,  34  are inclined obliquely to one another such that the interlock lever  30  is generally “L” shaped. The first arm  33  has a face  35  abutting the outer end  29  of the trigger  18  and the second arm  34  has a tip  36  that projects into the mouth  22  and is complementary to the third and fourth recesses  25   c,    25   d.  A torsion spring  37  has a helical portion disposed generally coaxially with the fulcrum shaft  32  and urges the interlock lever  30  to rotate towards its unlocking position shown in  FIG. 2 , urging the face  35  against the outer end  29  of the trigger. When the trigger  18  is squeezed and pivoted toward its retracted position this engagement with the interlock lever  30  rotates the interlock lever to its locking position (shown in dashed outline in  FIG. 2 ), in which the tip  36  is inserted into the recess  25   c.    
         [0027]    In use, the latch  20  is pressed to permit rotation of the handle  10  relative to the motor housing  12  without the need to operate any other device for connecting the handle and motor housing  12 . This permits the handle  10  to be very readily rotated as the use dictates. When the trigger  18  is pressed the interlock mechanism  22  provides a back up to the latch  20 , and maintaining the fixed relation between the handle  10  and motor housing  12  in case the latch  20  is mistakenly operated when the tool is being operated. 
         [0028]    In addition, with the tool not in use and the handle  10  is not in one of its operating positions, the interlock lever  30  is misaligned with either of the recesses  25   c,    25   d.  A small movement of the trigger  18  serves to press the tip  36  of the interlock lever  30  against the concave surface  40  that spans between the third and fourth recesses  25   c,    25   d.  In this position the switch  30  is not yet actuated to start the motor and the trigger  18  is blocked by the unlock lever  30  and is unable to pivot to its locking position, in which case the interlock lever  30  prevents the trigger  18  being depressed, except in the operating positions defined by the recesses  25   a - 25   d.  This prevents the tool being started up in an unsafe condition, in which the handle  10  is free to rotate. 
         [0029]    Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.