Abstract:
A hammer drill comprises: a body, a motor; a centre of gravity, a hammer mechanism driven by the motor in reciprocating movement along a hammer axis at a first distance from the centre of gravity, a counter mass mounted within the body for sliding movement along a slide axis at a second further distance from the centre of gravity; and a biasing member which biases the counter mass to a mid-position along the slide axis. The biasing means may be a leaf spring or a helical spring. The counter mass may be slideably supported on rods and may be able to twist about a number of axes.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to hammer drills, and in particular, to vibration dampening in hammer drills.  
       BACKGROUND OF THE INVENTION  
       [0002]     A typical hammer drill comprises a body attached to the front of which is a tool holder in which a tool bit such as a chisel or a drill bit is capable of being mounted. Within the body is a motor which reciprocatingly drives a piston mounted within a cylinder via a wobble bearing or crank. The piston reciprocatingly drives a ram which repetitively strikes a beat piece which in turn hits the rear end of the chisel of tool bit in well known fashion. In addition, in certain types of hammer drill, the tool holder can rotationally drive the tool bit.  
         [0003]     EP1157788 discloses an example of a typical construction of a hammer drill.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     The reciprocating motion of the piston, ram and striker to generate the hammering action cause the hammer to vibrate. It is therefore desirable to minimise the amount of vibration generated by the reciprocating motion of the piston, ram and striker.  
         [0005]     Accordingly, there is provided a hammer drill comprising:  
         [0006]     a body in which is located a motor;  
         [0007]     a tool holder capable of holding a tool bit;  
         [0008]     a hammer mechanism, driven by the motor when the motor is activated, for repetitively striking an end of the tool bit when the tool bit is held by the tool holder  6 ;  
         [0009]     a counter mass slideably mounted within the body which is capable of sliding in a forward and rearward direction between two end positions;  
         [0010]     biasing means which biases the counter mass to a third position located between the first and second positions;  
         [0011]     wherein the counter mass is located above the centre of gravity of the hammer;  
         [0012]     the mass of the counter mass and the strength of the biasing means being such that the counter mass slidingly moves in forward and rearward direction to counteract vibrations generated by the operation of the hammer mechanism. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     Four embodiments of the present invention will now be described with reference to the accompanying drawings of which:— 
         [0014]      FIG. 1  shows a perspective view of hammer drill;  
         [0015]      FIG. 2  shows a first embodiment of the anti-vibration mechanism;  
         [0016]      FIG. 3  shows the second embodiment of the anti-vibration mechanism;  
         [0017]      FIG. 4  shows a side view of the third embodiment of the anti-vibration mechanism;  
         [0018]      FIG. 5  shows a close-up of a leaf spring of the third embodiment;  
         [0019]      FIG. 6  shows a downward perspective view of the third embodiment;  
         [0020]      FIG. 7  shows a second downward perspective view of the third embodiment;  
         [0021]      FIG. 8  shows a perspective view of the fourth embodiment of the anti-vibration mechanism;  
         [0022]      FIG. 9  shows a side view of the anti-vibration mechanism of the fourth embodiment;  
         [0023]      FIG. 10  shows a side view of the vibration counter mass mechanism, with the metal weight twisted about a horizontal axis, with the springs omitted;  
         [0024]      FIG. 11  shows a top view of the anti-vibration mechanism, with the metal weight slid to one side (right), with the springs omitted;  
         [0025]      FIG. 12  shows a top view of the anti-vibration mechanism, with the metal weight twisted about a vertical axis, with the springs omitted;  
         [0026]      FIG. 13A  shows half of the anti-vibration mechanism, with the metal weight slid to one side (right);  
         [0027]      FIG. 13B  shows a vertical cross section of the anti-vibration mechanism in  FIG. 13A  in the direction of Arrows C;  
         [0028]      FIG. 14A  shows half of the anti-vibration mechanism, with the metal weight slid to one side (right) further than that shown in  FIG. 13A ;  
         [0029]      FIG. 14B  shows a vertical cross section of the anti-vibration mechanism in  FIG. 14A  in the direction of Arrows D;  
         [0030]      FIG. 15  shows a top view of the anti-vibration mechanism mounted on the top section of a hammer;  
         [0031]      FIG. 16  shows a perspective view of the anti-vibration mechanism mounted on the top section of a hammer;  
         [0032]      FIG. 17  shows a perspective view of the anti-vibration mechanism mounted on the top section of a hammer with part of the outer casing covering the vibration mechanism;  
         [0033]      FIG. 18  shows a sketch of the front of the metal weight; and  
         [0034]      FIG. 19  shows a sketch side view of the metal weight. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     Referring to  FIG. 1 , the hammer drill comprises a body  2  in which is located a motor (not shown) which powers the hammer drill. Attached to the rear of the body  2  is a handle  4  by which a user can support the hammer. Mounted on the front of the body  2  is a tool holder  6  in which a drill bit or chisel (not shown) can be mounted. A trigger switch  8  can be depressed by the operator in order to activate the motor of the hammer in order to reciprocatingly drive a hammer mechanism located within the body  2  of the hammer. Designs of the hammer mechanism by which the reciprocating and/rotational drive for the drill bit or chisel are generated from the rotational drive of the motor are well known and, as such, no further detail will be provided.  
         [0036]     The first embodiment of the present invention will now be described with reference to  FIG. 2 .  
         [0037]     Referring to  FIG. 2 , the first embodiment of the anti-vibration mechanism is shown. The top section  10  (see  FIG. 1 ) of the housing  2  is in the form of a metal cast. The top section  10  is attached to a middle section  12  which in turn is attached to a lower section  14  as best seen in  FIG. 1 . The top section  10  encloses the hammer mechanism (of typical design) including a crank (not shown) which is located within a rear section  16  of the top section  10 , a piston, ram and striker, together with a cylinder in which they are located, none of which are shown. The reciprocating motion of the piston, ram and striker within the cylinder causes the hammer to vibrate in a direction approximately parallel to the direction of travel of the piston, ram and striker. It is therefore desirable to minimise the amount of vibration generated by the reciprocating motion of the piston, ram and striker.  
         [0038]     Rigidly attached to the top of the top section  10  are two metal rods  18  which run lengthwise along the top of the top section  10 . The rear ends of the rods  18  connect to the top section  10  via a support  13  which is screwed into the top section  10 . The front ends of the rods  18  pass through a bore in the top section  10  and then through a flange  17  in a front section  15  of the housing  2 , which attaches to the forward end of the top section  10 . Nuts  19  are screwed onto the end of the rods  18  to secure them to the front and top sections  10 ,  15 . The rods  18  also perform the function of assisting the rigid connection between the front section  15  and the top section  10 .  
         [0039]     Mounted on the two rods is a metal weight  20  which is capable of freely sliding backwards and forwards along the two rods  18  in the direction of Arrow E. Four springs  22  are mounted on the two rods  18  between the metal weight  20  and the two ends of the rods  18  where they are attached to the upper section  10 . As the body  2  of the hammer vibrates, the metal weight  20  slides backwards and forwards along the two rods  18  compressing the various springs  22  as it moves backwards and forwards. The mass of the metal weight  20  and the strength of the springs  22  have been arranged such that the metal weight  20  slides backwards and forwards out of phase with the movement of the body of the hammer and as such counteracts the vibrations generated by the reciprocating movement of the piston, ram and striker. Thus, with the use of the correct weight for the metal weight  20  and strength of springs  22 , the overall vibration of the tool can be reduced.  
         [0040]     The anti-vibration mechanism is enclosed by an outer cap  11  (see  FIG. 1 ) which attaches to the top of the top section  10 .  
         [0041]     The motor is arranged so that its spindle is vertical and is generally located within the middle  12  section. As a large proportion of the weight of the hammer is caused by the motor, which is located below the cylinder, piston, ram and striker, the centre of mass  9  is lower than the longitudinal axis of the cylinder, piston, ram and striker.  
         [0042]     The vibration forces act on the hammer in a direction which is coaxial to the axis  7  of travel of the piston, ram and striker. Movement of the metal weight  20  along the rods  18  will counteract vibration in the hammer in a direction parallel to axis  7  of travel of the piston, ram and striker.  
         [0043]     As the centre of mass  9  of the hammer is below the axis  7  of travel of the piston, ram and striker, there will also be a twisting moment (Arrow F) about the centre of gravity  9  caused by the vibration. As the sliding metal weight  20  is located above the centre of gravity  9 , the sliding movement will also counter the twisting moments (Arrow F) about the centre of gravity  9  caused by the vibration.  
         [0044]      FIG. 3  shows a second embodiment of the anti-vibration mechanism.  
         [0045]     This embodiment operates in a similar manner as the first embodiment. Where the same features are present in the second embodiment which are present in the first embodiment, the same reference numbers have been used.  
         [0046]     The difference between the first and second embodiment is that the metal weight  20  is now mounted to the top section  10  by the use of a single leaf spring  24  which connects between the metal weight and the top section  10  and supports the metal weight  20  on the tope section  10 . The metal weight  20  slides backwards and forwards in the direction of Arrows E in the same manner as in the first embodiment. However, due to the shape of the leaf spring  24  which is attached to the front  26  of the metal weight  20  then wraps around the metal weight  20  to the rear  28  of the metal weight  20  the centre  30  of which being attached to the top section  10 , enable the metal rods to be dispensed with as the leaf spring  24  in the forwards and backwards direction, produces a resilient affect, whilst preventing the metal weight  20  from rocking in a sideways direction. This simplifies the design considerably and reduces cost. Furthermore, the use of a leaf spring  24  allows some twisting movement of the metal weight  20  about a vertical axis of rotation.  
         [0047]     A third embodiment of the present invention is shown in  FIGS. 4, 5 ,  6  and  7 .  
         [0048]     This embodiment operates in a similar manner as the second embodiment. Where the same features are present in the third embodiment which are present in the second embodiment, the same reference numbers have been used.  
         [0049]     Referring to these figures, the single leaf spring of the second embodiment has been replaced by two leaf springs  32 ,  34 . The first leaf spring  32  which connects to the front  36  of the metal weight  20  also connects to the upper section  10  forward metal weight  20 . The second leaf  34  spring connects to the rear  38  of the metal weight  20  which then connects to the top section, to the rear of the metal weight  20 . The metal weight  20  can oscillate backwards and forwards as with the other two embodiments but is prevented from sideward movement due to the rigidity of the leaf springs  32 , 34 .  
         [0050]     In order to improve the performance of the leaf springs  32 , 34 , each of the two leaf springs  32 , 34  are constructed from two layers  40 , 42  of sheet metal as best seen in  FIG. 5 . The two sheets of metal  40 , 42  are located on top of each other as shown. This provides an improved damping performance when used in this application. It also provides better support for the metal weight and improves the damping efficiency.  
         [0051]     FIGS.  8  to  19  shows a fourth embodiment of the anti-vibration mechanism.  
         [0052]     This embodiment operates in a similar manner as the first embodiment. Where the same features are present in the fourth embodiment which are present in the first embodiment, the same reference numbers have been used.  
         [0053]     A metal weight  50  is slideably mounted on two rods  52 , the ends of which terminate in metal rings  54 . The metal rings  54  are used to attach the rods  52  to the top section  10  of the housing  2  using screws  56  which pass through the rings  54  and are screwed into the top section  10 . A cross bar  58  attaches between each pair of rings  54  as shown to provide a structure as shown.  
         [0054]     Two sides of the metal weight  50  comprise a supporting mount  60  which are each capable of sliding along one of the rods  52 . A spring  62  is located between each end of the rods  52  adjacent the rings  54  and a side of the supporting mounts  60 . The four springs cause the metal weight  50  to slide to the centre of the rods  52 . The springs are compressed. The ends of the springs adjacent the rings are connected to the ends of the rod. The other ends, abutting the supporting mounts are not connected to the supporting mounts, but are merely biased against them by the force generated by the compression of the springs.  
         [0055]     As the hammer vibrates, the metal weight can slide backward and forwards along the rods out of phase with the vibrational movement of the vibrations of the hammer to counteract the effects of the vibrations.  
         [0056]     The supporting mounts  60  are designed in such a manner that they comprise a sideways facing vertical C shaped slot  64  as best seen in the sketch  FIG. 18  (not enclosed electronically). This provides for easy assembly. It also allows the metal weight  50  to twist in direction of Arrow A in Figure as it slides along the rods  52 . This enables the metal weight  50  to twist about a vertical axis  74  enabling it to counteract vibrations in a direction other than parallel to the longitudinal axis  66  of the spindle.  
         [0057]     The supporting mounts  60  are also designed in such a manner that they comprise a sideways horizontal slot  68  as best seen in the sketch  FIG. 19  (not enclosed electronically). The two sides  70  of the horizontal slot  68  are convex as shown in the sketch. This also provides for easy assembly. It also allows the metal weight  50  to twist in the direction of Arrow B in  FIG. 19  whilst it is mounted on the rods  52 . This enables the metal weight to twist about a horizontal axis  72  which is roughly perpendicular to the longitudinal axes of the rods  52 . This also allows the metal weight  50  to counteract vibrations in a direction other than parallel to the longitudinal axis  66  of the spindle.  
         [0058]      FIG. 13A  shows the metal weight  50  when it is slid around approximately 66% along the length of the rods  52  towards the right. The left hand springs  62  are larger in length due to being allowed to expand. The right hand springs  62  are shorter in length due to being compressed by the movement of the metal weight  50 . However, in this position, the ends of the springs  62  abut against the sides of the supporting mounts  60  due to the force of the springs  62  as they are compressed. However, if the metal weight  50  is slid further along the length of the rods  52  towards the right, the left hand spring  62  disengages with the side of the supporting mount  60  due to the length of the spring  62  being shorter than the length of rod  52  along which the metal weight  50  can travel. This results in the right hand spring  62  only being in contact with the supporting mounts  60 . As such, as the metal weight  50  slides right as shown in  FIG. 13A  until the right hand springs  62  become fully compressed, only one spring  62  per rod  52  providing a dampening force on the metal weight  50 . This alters the spring characteristics of the vibration dampener. This enables the spring dampener to be designed so that, when the vibrations on the hammer are at their most extreme and metal weight  50  is travelling at the greatest distance from the centre of the rods  52  along the length of the rods  52 , the spring characteristics can be altered when the metal weight  50  is at its most extreme positions to counteract this.