Abstract:
A hammer drill, in particular a chipper comprising: a body  2  having at least one support handle  4 ; an electric motor mounted within the body  2 ; an electric switch  22 , capable of being switched on and off by a trigger button  8  connected to it, to activate or deactivate respectively the electric motor, wherein the trigger button  8  is moveable between two positions, a first position where the electric switch  22  is off and a second position where the electric switch  22  is on; a locking arm  38  moveably mounted on the electric switch  22  which, when the trigger button  8  is located in its second position, is moveable between two positions, a first position where it is disengaged from the trigger button  8  and a second position where it engages with the trigger button  8  and holds the trigger button  8  in its second position. When the locking arm is in its second position it causes the hammer to remain switch on even if the operator removes their fingers from the trigger button.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a hammer drill and in particular, a chipper.  
       BACKGROUND OF THE INVENTION  
       [0002]     A chipper is a power tool which is used to chisel a workpiece such a block of stone. Typically, such chippers are powered by an electric motor which are either powered by a mains electricity power supply or by a battery. A tool bit, usually in the form of a chisel, is mounted in a tool holder located at the front of the chipper. The tool holder prevents the tool bit from rotation. However, the tool bit is capable of axially sliding within the tool holder over a limited range of movement.  
         [0003]     The electric motor is activated by depression of the trigger switch which is usually mounted on a handle attached to the body of the chipper. The electric motor reciprocatingly drives a striker via gears, a rotary to linear movement conversion mechanism, typically a crank or wobble bearing, and an air spring, typically in the form of a piston, cylinder and ram, mounted within the chipper in well-known manner. The striker repeatedly hits the end of the drill bit located within the tool holder causing the tool bit to be repeatedly driven forwards. In use, the cutting tip the tool bit is placed against the work piece to be chiseled. The striker repeatedly hits end of the tool bit within the tool holder, causing tool bit to chip or chisel away at the work piece.  
         [0004]     Ideally, such chippers can operate in two modes of operation.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     The first mode of operation is where depression of the trigger switch by an operator causes the motor to be activated. The operator can then use the chipper whilst the trigger switch remains depressed. In order to keep the electric motor activated, the operator must keep the trigger switch depressed. Upon release of the trigger switch, the electric motor is deactivated and the chipper is switched off.  
         [0006]     In the second mode of operation, the chipper can be “locked on”. This means that once the trigger switch has been depressed and the electric motor activated, the chipper can be “locked on” so that the electric motor remains constantly activated even when the operator releases the trigger switch. This enables the operator to move their hands around the handle and body of the chipper to support it in different places whilst the chipper remains activated. Once the operator wishes to stop the chipper, the “lock on” is switched off, allowing the electric motor to be deactivated when the trigger switch is released. If the “lock on” is switched off whilst the trigger switch is not depressed, the motor stops immediately.  
         [0007]     Accordingly there is provided a hammer drill comprising:  
         [0008]     a body having at least one support handle;  
         [0009]     an electric motor mounted within the body;  
         [0010]     an electric switch, capable of being switched on and off by a trigger button connected to it, to activate or deactivate respectively the electric motor, wherein the trigger button is moveable between two positions, a first position where the electric switch is off and a second position where the electric switch is on;  
         [0011]     a locking arm moveably mounted on the electric switch which, when the trigger button is located in its second position, is moveable between two positions, a first position where it is disengaged from the trigger button and a second position where it engages with the trigger button  8  and holds the trigger button in its second position.  
         [0012]     Though the embodiment below relates to a chipper, it is clear to a person skilled in the art that the invention is applicable to any type of hammer drill. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     An embodiment of the present invention will now be described with reference to the accompanying drawings of which:  
         [0014]      FIG. 1  shows a front perspective view of a hammer drill;  
         [0015]      FIG. 2  shows a rear perspective view of a hammer drill  
         [0016]      FIG. 3  shows the rear clam shell of the chipper with the sliding “lock on” activator;  
         [0017]      FIG. 4  shows part of the rear clam shell with the electric switch, the trigger button, the pivotal latch and the sliding “lock on” activator;  
         [0018]      FIG. 5  shows the trigger button, the pivotal latch and the sliding “lock on” activator;  
         [0019]      FIG. 6  shows the trigger button, the pivotal latch with biasing spring;  
         [0020]      FIG. 7  shows the electric switch and the trigger button;  
         [0021]      FIG. 8  shows the inside of the trigger button with the catch;  
         [0022]      FIG. 9  shows the underside of the sliding “lock on” activator;  
         [0023]      FIG. 10  shows the rear of the trigger button with the sliding “lock on” activator; and  
         [0024]      FIG. 11  shows part of the rear clam shell with the electric switch, the pivotal latch and the sliding “lock on” activator. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Referring to  FIGS. 1 and 2 , the chipper comprises a body  2  attached to the rear of which is a rear support handle  4 . An electric motor (not shown) is mounted within the body. The electric motor is powered by a mains electricity power supply (not shown).  
         [0026]     Mounted on the front of the body  2  of chipper is a tool holder  6 . A chisel (not shown) can be mounted in the tool holder  6 . The tool holder prevents the chisel from rotation. However, the chisel is capable of axially sliding within the tool holder  6  over a limited range of movement.  
         [0027]     The electric motor is activated by depression of a trigger button  8  which is mounted on the inside of the rear support handle  4 . The electric motor reciprocatingly drives a striker (not shown) via gears (not shown) and a wobble bearing (not shown) and an air spring in the form of a piston, cylinder and ram (not shown) mounted within the body  2  of the chipper in well-known manner. The striker repeatedly hits the end of a chisel located within the tool holder  6  causing the chisel to be repeatedly driven forwards. In use, the cutting tip the chisel is placed against the work piece to be chiseled. The striker repeatedly hits end of the chisel within the tool holder  6 , causing chisel bit to chip or chisel away at the work piece.  
         [0028]     The chipper can operate in two modes of operation.  
         [0029]     The first mode of operation is where depression of the trigger button  8  by an operator causes the motor to be activated. The operator can then use the chipper whilst the trigger button  8  is depressed. In order to keep the electric motor activated, the operator must keep the trigger button  8  depressed using their fingers. Upon release of the trigger button, the electric motor is deactivated and the chipper is switched off.  
         [0030]     In the second mode of operation, the chipper can be “locked on”. This means that once the trigger button  8  has been depressed and the electric motor activated, the chipper can be “locked on” so that the electric motor remains constantly activated even when the operator releases the trigger button  8 . This enables the operator to move their hands around the body  2  and rear support handle  4  of the chipper to support it in different places whilst the chipper remains activated. Once the operator wishes to stop the chipper, the “lock on” is switched off, allowing the electric motor to be deactivated when the trigger button  8  is released.  
         [0031]     The “lock on” is switched on by the sliding movement of a sliding “lock on” activator  10 . The sliding “lock on” activator comprises a bar which is located within the top section  12  of the rear support handle  4  and which extends through the sides of the rear clamshell which forms the rear support handle  4 . One end  14  of the bar extends through an aperture formed in one side (shown in  FIG. 1 ) of the rear support handle  4 , the other end  16  extends through a second aperture formed in the opposite side (shown in  FIG. 2 ) of the rear support handle  4 , the two ends  14 ,  16  being visible externally whilst the centre section of the bar remains internally within the top section  12  of the rear support handle  4 . The bar can slide axially within the top section  12  of the rear support handle across the width of the rear support handle  4  from a first position where one end  14  projects substantially from one side of the chipper to a second position where the other end  16  projects substantially from the other side of the chipper, and then back to the first position.  
         [0032]     The mechanism by which the chipper is “locked on” will now be described in detail with reference to FIGS.  3  to  11 .  
         [0033]     Referring to  FIG. 3 , the rear support handle is formed from a plastic clamshell  18 . Mounted within the rear support handle  4  is an electric switch  22  as best seen in FIG.  4 . Connected to the electric switch  22  is the trigger button  8 . The trigger button  8  connects to the electric switch  22  via an elongate rod  24  of circular cross-section. The elongate rod  24  is capable of being axially slid along its elongate axis over a limited range of movement. Depression of the trigger button  8 , so that it moves into the rear support handle  4 , causes the elongate rod  24  to move along its elongate axis and be pushed into the body of the electric switch  22  causing the electric switch to make an electrical connection thus allowing electric current to pass through it which in turn activates the electric motor.  
         [0034]      FIG. 6  shows the elongate rod  24  connecting into the rear of the trigger button  8 .  FIG. 8  shows a rear view of the trigger button  8  together with a recess  26  of circular cross section in which the end of the elongate rod  24 , which projects from the electric switch  22 , locates and connects to the trigger button  8 . The elongate rod is biased outwardly from the body of the electric switch  22  via a spring (not shown) within the electric switch  22  to a maximum outward position. When the elongate rod  24  extends to its maximum position due to the biasing force of the spring, the electric switch  22  is switched off, with no electric current being able to pass through the switch  22 . Depression of the trigger button  8  moves the elongate rod  24  against the biasing force of the spring into the body of electric switch  22  switching the electric switch  22  on.  
         [0035]     The sliding “lock on” activator  10  will now be described in detail.  
         [0036]     The sliding “lock on” activator (indicated by reference number  10  in  FIG. 1 ) comprises a bar as best seen in  FIGS. 4 and 5  which has a central section  28 , and two ends  14 ,  16 . The bar, as described previously, extends through the top section  12  of the rear support handle  4 , the two ends  14 ,  16  projecting through apertures formed in the clamshell  18  which forms the rear support handle  4 . The bar is capable of sliding within the clam shell  18  into and out of the apertures, along its longitudinal axis.  
         [0037]     The bar is mounted transversely across a support rod  30 , the longitudinal axis of the bar being substantially perpendicular to that of the support rod  30 . When the sliding “lock on” activator  10  is mounted within the top section  12  of the rear support handle  4 , both the longitudinal axes of the support rod  30  and of the bar are substantially horizontal. The bar is mounted part way along the length of the support rod  30  as shown in the  FIGS. 4 and 5 .  
         [0038]     The movement of the bar and support rod  30  is controlled by the bar which is capable of sliding along its longitudinal axis only. Thus the support rod  30  is only capable of sliding width ways, horizontally from left to right within the clam shell  18 . The support rod  30  limits the amount of sliding movement of the bar  28 .  
         [0039]     Attached to one end of the support rod  30  is a circular disk  32  as shown. The circular disk  32  is provided as a grip by which a person assembling the chipper can hold the “lock on” mechanism during production. The circular disk performs no function in the operation of the “lock on” mechanism when the tool is assembled.  
         [0040]     Formed in the other end of the support rod  30  opposite to that to which the circular disk  32  is attached, is a U-shaped recess  36 .  
         [0041]     The sliding “lock on” activator  10  comprising the bar, the support rod  30  with the U-shaped recess  36  and circular disk  32  are formed from plastic in a one-piece construction.  
         [0042]     The pivotal latch  38  with biasing spring  46  will now be described in detail with reference to the figures.  
         [0043]     The pivotal latch is best seen in  FIG. 6 . The pivotal latch comprises a central pivot mount  40  of circular cross-section about the longitudinal axis  42  of which the pivotal latch  38  is capable of pivoting.  
         [0044]     Extending from one side of the pivot mount  40  substantially perpendicular to the longitudinal axis  42  of the pivot mount  40 , is a first arm  44 . Attached to the side of the first arm  44  is a helical spring  46  the axis of which extends substantially perpendicular to the longitudinal axis of the first arm  44  and to the longitudinal axis  42  of the pivot mount  40 .  
         [0045]     Extending from the other side of the pivot mount  40  in the opposite direction to the first arm  44  is a second arm  48 . The second arm  48  extends in a direction which is substantially parallel to the first arm  44 . Mounted on the topside of the second arm  48 , towards the end of the second arm  48 , remote from the pivot mount  40 , is a drive peg  50 . The drive peg  50  is substantially circular in cross-section and extends in a direction parallel to that of the longitudinal axis  42  of the pivot mount  40 . Mounted on the underside of the second arm  48  towards the end of the second arm  48  remote from the pivot mount  40 , is a latch arm  52 . The latch arm  52  extends downwardly in the opposite direction to the drive peg  50  but substantially parallel to it.  
         [0046]     Referring to  FIG. 7 , the top of the body of the electric switch  22  comprises a tubular recess  54  of circular cross-section. The longitudinal axis  56  of the tubular recess  54  is vertical.  
         [0047]     The underside of the pivot mount  40  locates within the tubular recess  54  of the electric switch  22  such that the two axes  42 ,  56  are coaxial. The pivotal latch  38  is capable of pivoting about the longitudinal axis  42  of the pivot mount  40  within the tubular recess  54  of electric switch  22 . The free end of the helical spring  46  which is attached to the first arm  44  attaches to the side of the body of electric switch  22  as shown in  FIG. 7 . The helical spring  46  biases the end of the first arm  44  away from the side of the body of the switch  22 .  
         [0048]     The drive peg  50  mounted on the topside of the second arm  48  locates within the U-shaped recess  36  formed in the support rod  30  of the “lock on” activator as best seen in  FIG. 4 .  
         [0049]     When an operator slides the bar  28  of the “lock on” activator  10 , the “lock on” activator  10  slides width ways within the clam shell  18  causing the U-shaped recess  36  formed in the end of the support rod  30  to move from left-to-right (or vice-versa). This in turn causes the drive peg  50  which is located within the U shaped recess  36  to move from left-to-right (or vice versa) as shown in  FIG. 6  causing the pivotal latch  38  to pivot about the longitudinal axis  42  of the pivot mount  40 . Movement of the pivotal latch  38  causes compression or expansion of the helical spring  46  connected between the first arm  44  the pivotal latch  38  on the body of the electrical switch  22 .  
         [0050]     The pivotal latch  38  is made from plastic in a one piece construction.  
         [0051]     Referring to  FIG. 8 , it can be seen that the trigger button  8  is hollow. A horizontal shelf  60  is formed across the width of the inside of the trigger button  8  approximately halfway up within the trigger button  8 . Formed on the top surface of the shelf  60  is a catch  62 . The catch  62  comprises an elongate ridge  64  which extends forward within the trigger button  8 . Formed adjacent to one end of the elongate ridge  64  is a second smaller ridge  66  which extends sideways, perpendicular to that of the elongate ridge  64 . A chamfer  68  is formed on the corner of the elongate ridge  64  at the same end as that from which the smaller ridge  66  extends, on the opposite side from that which the smaller ridge  66  extends. The junction of the smaller ridge  66  and the forward end of the elongate ridge  62  forms a recess  70 .  
         [0052]     Formed on the bottom end of the latch arm  52  is a stop  72  as shown in  FIG. 9 . When the pivotal latch  38  is mounted on the electrical switch, the latch arm  52  extends into the inside space of the trigger button  8  formed by the inner walls  74  of the trigger button  8  and the shelf  60 . When the pivotal latch  38  is pivoted due to the sliding movement of the bar  28  of the “lock on” activator  10 , the latch arm  52  pivots inside the trigger button. The height of the stop  72  within the trigger button  8  is a same as that of the catch  62  such that pivotal movement of the latch arm  52  causes the stop  72  to engage with the side of the catch  62 .  
         [0053]     When the chipper is switched off with trigger button  8  located by its maximum amount away from the electrical switch  22 , the latch arm  52  is located to the right to the catch  62  as shown in  FIG. 8  such that it is on the opposite sides to the elongate ridge  64  of the catch  62  to that of smaller ridge  66 . In this position, the “lock on” mechanism is switched off and the chipper only operates in the first mode of operation. When an operator tries to pivot the latch arm  52  by a sliding movement of the bar, the stop  72  engages the side of the catch thus preventing movement of the latch arm  38  and hence the pivotal latch  38 . This in turn blocks the sliding movement of the “lock on” activator  10  and thus the bar which forms part of it. Thus the chipper is prevented from starting the second mode, namely the “lock on” mode whilst the chipper is switched off.  
         [0054]     When the trigger button  8  is depressed, the trigger button  8 , together with the catch  62 , is move towards the electrical switch  22 . However the latch arm  52  remains stationary as it is mounted on the electrical switch  22 . Thus the relative position of the latch arm  52  within the trigger button  8  moves. When the trigger button has been depressed sufficiently, the catch  62  will move sufficiently towards the electrical switch  22  that the stop  72  of the latch alarm  52  is able to pass around the forward end of the catch  62 . At this point, the operator can slidingly move the bar  28  causing the pivotal latch  38  to pivot against the biasing force of the spring  46  causing the latch arm  52  to pivot within the inside of the trigger button  8  around the top end of the catch. Upon release of the trigger button  8  whilst the latch arm  52  is in this position, the stop  72  locates within the recess  70  of the catch  62  thus preventing the trigger button  8  from returning to its opposition. Whilst the stop  72  remains in this position, the trigger button  8  is held in an inward position thus maintaining the chipper activated in the second mode of operation, with the electrical switch constantly activated even when the operator removes the fingers from the trigger button  8 . The latch arm  52  is prevented from pivoting backwards due to the biasing force of the spring  46  by the stop  72  being held within the recess  70 .  
         [0055]     In order to release the “lock on”, the operator depresses the trigger button  8  which moves the stop  72  from the recess  70 . This allows the latch arm  52  to pivot across the top of the catch  62  due to the biasing force of the spring  46  (unless it is held there by the operator preventing the bar from moving position) and locate on the right of the catch as shown in  FIG. 8 . Then, upon release the trigger button  8 , the trigger button  8  can move to allow electrical switch  22  to be switched off.