Abstract:
A hammer comprising: a body; a tool holder mounted on the body for holding a cutting tool; a handle pivotally mounted on the body about an axis; a vibration dampener which connects between the handle and the body and which reduces the amount of angular vibrations transmitted from the body to the handle; a motor mounted within the body; a hammer mechanism mounted in the body, capable of being driven by the motor when the motor is activated, the hammer mechanism, when driven, imparting impacts onto a cutting tool  6  when held by the tool holder; wherein the handle is pivotally mounted about a pivot axis which passes through the centre of gravity of the hammer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority, under 35 U.S.C. §119(a)-(d), to UK Patent Application No. GB 08 049 63.7 filed Mar. 18, 2008, the contents of which is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a hammer and in particular, to a handle for a hammer. 
     BACKGROUND OF THE INVENTION 
     One type of hammer, often referred to as a hammer drill, can have three modes of operation. Such a hammer typically comprises a spindle mounted for rotation within a housing which can be selectively driven by a rotary drive arrangement within the housing. The rotary drive arrangement is driven by a motor also located within the housing. The spindle rotatingly drives a tool holder of the hammer drill which in turn rotatingly drives a cutting tool, such as a drill bit, releasably secured within it. Within the spindle is generally mounted a piston which can be reciprocatingly driven by a hammer drive mechanism which translates the rotary drive of the motor to a reciprocating drive of the piston. A ram, also slideably mounted within the spindle, forward of the piston, is reciprocatingly driven by the piston due to successive over and under pressures in an air cushion formed within the spindle between the piston and the ram. The ram repeatedly impacts a beat piece slideably located within the spindle forward of the ram, which in turn transfers the forward impacts from the ram to the cutting tool releasably secured, for limited reciprocation, within the tool holder at the front of the hammer drill. A mode change mechanism can selectively engage and disengage the rotary drive to the spindle and/or the reciprocating drive to the piston. The three modes of operation of such a hammer drill are; hammer only mode, where there is only the reciprocating drive to the piston; drill only mode, where there is only the rotary drive to the spindle, and; hammer and drill mode, where there is both the rotary drive to the spindle and reciprocating drive to the piston. 
     EP1157788 discloses such a hammer. 
     Another type of hammer only has a hammer only mode and which is more commonly referred to as a chipper. EP1640118 discloses such a chipper. 
     A third type of hammer will have hammer only mode and hammer and drill mode. GB2115337 discloses such a hammer. In GB2115337, the hammer mechanism comprises a set of ratchets which, when the drill is in hammer and drill mode, ride over each other to create vibrational movement which is superimposed on the rotary movement of the tool holder, thus imparting impacts onto a tool held by the tool holder. 
     BRIEF SUMMARY OF THE INVENTION 
     However, all types of hammer will have a hammer mechanism which, when activated, will impart impacts to a cutting tool when held in the tool holder. 
     Accordingly there is provided a hammer comprising: 
     a body; 
     a tool holder mounted on the body for holding a cutting tool; 
     a handle pivotally mounted on the body about an axis; 
     a vibration dampener which connects between the handle and the body and which reduces the amount of angular vibration transmitted from the body to the handle; 
     a hammer mechanism mounted in the body, capable of being driven by the motor when the motor is activated, the hammer mechanism, when driven, imparting impacts onto a cutting tool when held by the tool holder; 
     wherein the handle is pivotally mounted about a pivot axis which passes through the centre of gravity of the hammer. 
     By mounting the handle about an axis of pivot which passes through the centre of gravity, the handle is able to be damped against the rotational forces in an optimum manner as the rotational movement of the body due to the rotational forces generated by the vibrations and the pivotal movement of the handle are both about the centre of gravity. 
     The vibration dampener can comprises biasing means, such as a spring, which connects between the handle and the body and which biases the handle towards a predetermined angular position. The biasing means damps the rotary vibration about the centre of gravity and thus reduces the amount of vibration which is transferred to the handle from the body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Three embodiments of the present invention will now be described with reference to the accompanying drawings of which: 
         FIG. 1  shows a side view of the first embodiment of the present invention; 
         FIG. 2  shows a schematic diagram of the hammer mechanism of the hammer shown in  FIG. 1 ; 
         FIG. 2A  shows a schematic diagram of part on an alternative hammer mechanism to that shown in  FIG. 2 ; 
         FIG. 3  shows a top view of the hammer shown  FIG. 1 ; 
         FIG. 4  shows a side view of a hammer of the second embodiment of the present invention; 
         FIG. 5  shows a side view of a hammer of the third embodiment of the present invention; and 
         FIG. 6  shows a top view of the hammer shown  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 ,  2 , and  3 , the hammer comprises a body  2 . Mounted on the front of the body  2  is a tool holder  4  which is capable of holding a cutting tool  6 , such as a drill bit. Pivotally mounted on the body  2  is a handle  8  by which a user can support the hammer. 
     Mounted inside the body  2  is an electric motor  10  (see  FIG. 2 ) which is powered via a mains electric cable  12  via a trigger switch  14 . Depression of the trigger switch  14  activates the motor  10 . 
     The drive spindle  16  of the motor  10  drives a hammer mechanism (which is described in more detail below) via a number of gears  18 ,  20 ,  22 . A cylinder  24  of circular cross section is mounted within the body  2 . The longitudinal axis  26  of the cylinder  24  is coaxial with the longitudinal axis of a cutting tool  6  when held in the tool holder  4 . A beat piece support structure  28  is mounted within the body  2  between the cylinder  24  and the tool holder  4 . 
     As shown in  FIG. 2 , the hammer mechanism includes a crank mechanism which comprises a drive wheel  30  mounted eccentrically on which is a pin  32 . A piston  34  is slidingly mounted within the cylinder  24 . A rod  36  connects between the rear of the piston and the pin  32 . Rotation of the wheel  30  by the motor  10  via the gears,  18 ,  20 ,  22 , about its axis  38  results in rotation of the eccentric pin  32  around the axis of rotation  38  of the wheel  30 . This results in an oscillating movement of the piston  34  in the cylinder. An alternative design of hammer mechanism uses a wobble bearing  130  in stead of a crank as shown in  FIG. 2A . 
     The oscillating piston results in a reciprocating movement of the ram  36  within the cylinder due to the oscillating movement being transferred from the piston  34  to the ram  36  via an air spring  38 . The ram repeatedly strikes a beat piece  40 , slideably mounted within the beat piece support structure  28 , which in turn repeatedly strikes the end of a cutting tool  6  when held in the tool holder  4 . The axis along which the impact force is transferred to the end of the cutting tool is referred to as the drive axis. This is coaxial with the longitudinal axis  26  of the cylinder  24 . 
     The rear handle  8  comprises a grip portion  42  by which an operator grasps the handle  8  to support the hammer. The top  48  and bottom  50  of the grip portion  42  are attached via a central interconnecting section  110  to two identical triangular side panels  44 , which extend forward from the grip portion  42 , parallel to each other. Triangular holes  46  are formed through the side panels  44 . The tip  52  of each side panel  44  comprises a circular hole. A peg  54  is rigidly attached to the external wall of the body  2  on each side of the body  2 , the two pegs  54  being symmetrical. One peg  54  locates within the hole in the tip  54  of each panel  44 . The panels are slightly resilient, enabling them to be bent away from each other. This allows the tips  54 , during assembly of the hammer, of the two panels  44  to be bent away from each other, in order to pass over the two pegs  54  until the two holes in the tips  52  are aligned with the pegs  54 , and then released to allow the tips to move towards each other due to their resilient nature, allowing the pegs  54  to enter the holes and be retained within them. The panels  44 , and hence the handle  8  can freely pivot about the pegs  54 . 
     The mains cable  12  enters the lower end of the grip portion  42  of the handle  8  and passes internally until it connects to the trigger switch  14 . A second cable  56  then passes internally within the handle  8  until it reaches the lower end where it externally links across to the body  2  of the hammer and then internally within the body until it contacts the motor  10 . 
     A spring  58  connects between the top  48  of the grip portion  42  and the rear of the body  2 . The spring  58  biases the handle  8  to a predetermined position where the grip portion  42  is substantially vertical. The spring  58  can either be compressed or expanded, thus allowing the handle to pivot. Movement of the handle in the direction of Arrow A causes the spring  58  to compress, movement of the handle in the direction Arrow B causes the spring to expand. The handle can be pivoted away from its predetermined position against the biasing force of the spring  58 . However, when released, the handle would return to its predetermined position. 
     The hammer has a centre of gravity  60 . The construction and arrangement of the various components of the hammer results in the hammer having the centre of gravity  60  which is below (as seen in  FIG. 1 ) the drive axis  26 . 
     During use, the motor reciprocatingly drives the piston  34  which in turn reciprocatingly drives the ram  36  which in turn strikes the end of a cutting tool via the beat piece  40 . The sliding movement of the piston  34 , ram  36  and beat piece  40  is generally along the drive axis. The movement of the piston  34 , ram  36  and beat piece  40 , together with impact of ram against the beat piece, and the beat piece against the end of the tool bit  6  generate significant vibrations along the drive axis. Thus, the dominant vibrations of the hammer are in the direction of and aligned with the drive axis, which urge the body  2  to move in reciprocating manner along the drive axis  26 . As the centre of gravity  60  of the hammer is below the drive axis  26 , this reciprocating movement results in a rotational force F 1  to be experienced in the body of the hammer about the centre of gravity  60 , which in turn results in an angular reciprocating movement of the body  2  about the centre of gravity, as indicated by Arrow C, due to the vibrations. 
     The axis of pivot  62  of the handle  8  passes through the centre of gravity  60 . Furthermore, the axis of pivot  62  extends in a plane which is perpendicular to the drive axis  26  so that the vibrational forces along the drive axis  26  are tangential to the axis of pivot  62 . By mounting the handle  8  about an axis of pivot  62  which passes through the centre of gravity, the handle is able to be damped against the rotational forces (F 1 ; Arrow C) in an optimum manner as the rotational movement of the body  2  due to the rotational forces of the vibrations (F 1 ; Arrow C) and the pivotal movement of the handle are about the same axis. The spring  58  damps the rotary vibration (due rotational the force F 1 ; Arrow C) about the centre of gravity and thus reduces the amount of vibration which is transferred to the handle  8  from the body  2 . 
       FIG. 4  shows a second embodiment of the present invention. Where the same features are present in the second embodiment were present in the first, the same reference numbers have been used. The majority of the features present in the first embodiment are present in the second embodiment. The difference (described in more detail below) is that the handle  8  is slideably mounted on the pegs  54  to allow for damping in a direction parallel to the drive axis  26  in addition to damping against rotational vibrational movement about the centre of gravity  60 . 
     In the second embodiment, each panel  44  comprises an elongate hole  70  in which the corresponding peg  54  is located. This allows each peg  54  to slide in the X direction along the length of the hole  70 . However, the width of the elongate hole is marginally larger that the diameter of the pegs so that a sliding movement of the pegs within the elongate holes in a Y direction is prevented. 
     On each side of the body  2 , a front helical spring  72  (only one helical spring  72  and panel  44  are shown) is connected between an inner wall  74  of the body  2  and the tip  52  of a side panel  44 . Each helical spring  72  biases the tip  52  of its respective panel  44  rearwardly so that the peg  54  is located in its foremost position within the elongate hole  70 . The front springs  72  provide a biasing force between the body  2  and the handle  8 , urging them away from each other. When an operator grasps the grip portion  42  of the handle  8  and applies a pressure to the hammer during normal use, the handle  8  moves forward against the biasing force of the front springs  72 , the pegs  54  sliding rearwardly within the elongate holes  70 . The elongate holes  70  allow for relative movement between the body  2  of the hammer and the rear handle  8  in the X direction (indicated by Arrow D). The springs  72  absorbs vibrations generated in the body  2  in the X direction, reducing the amount transferred from the body  2  to the handle  8  in the X direction. 
     The panels  44  of the handle  8  can still freely rotate about the pegs  54 , and hence about an axis  62  which passes through the centre of gravity  60 . Each panel  44  has a centre stump  80  located at the rear of the panel  44 . Each centre stump  80  is connected via two rear helical springs  76 ,  78  to a rear wall  82  of the body (only one of the centre stumps  80  and its corresponding pair of springs  76 ,  78  are shown). As the handle  8  rotates about the pegs  54  in direction of Arrow E, the top spring  76  compresses and the bottom spring  78  expands, thus providing a resilient force against the pivotal movement of the handle  8 . As the handle  8  rotates about the pegs  54  in direction of Arrow F, the top spring  76  expands and the bottom spring  78  compresses, thus providing a resilient force against the pivotal movement of the handle  8 . The springs  76 ,  78  damp the rotary vibration (due rotational the force F 1 ; Arrow C) which is transferred to the handle  8  from the body  2 . The springs  76 ,  78  are arranged so that when no rotary force is applied to the handle  8 , the handle  8  is held in a position where the grip  42  is roughly vertical. 
     If the handle is moved in the X direction, against the biasing force of the front springs  72 , both of the rear springs  76 ,  78  are expanded to allow for the sliding movement of the handle  8  on the pegs  54 . However, both springs  76 ,  78  continue to provide a biasing force against any pivotal movement of the handle  8  even when they have been expanded slightly by the sliding movement of the handle  8  on the body  2 . As such, the rear springs  76 ,  78  provide a biasing force against pivotal movement of the handle  8  regardless of the position of the handle  8  on the body  2  (or pegs  54  within the elongate holes  70 ) and therefore provide rotational vibrational damping when the pegs  54  are at any position within the elongate holes  70 . 
     As the handle  8  slides forward and backwards, the rear springs  76 ,  78  will expand and contract, providing some damping in the X direction. However, as the amount of expansion of the rear springs  76 ,  78  due to the sliding movement of the pegs within the elongate holes  70  is relatively small, the amount of damping caused by the springs  76 ,  78  in the X direction will be relatively small. As such, the amount of damping in the X direction will be dominated by the front springs  72 . 
     Similarly, as the handle  8  pivots around the pegs  54 , the forward springs  72  will expand and contract providing some damping against the pivotal movement. However, the amount of expansion of the forward springs  72  due to the pivotal movement of handle  8  about the pegs  54  is small and therefore, the amount of damping caused by the front springs  72  in a pivotal direction will be relatively small. As such, the amount of damping of the pivotal movement of the handle  8  will be dominated by the rear springs  76 ,  78 . 
     Pivotally connected via a pivot mechanism to the lower side of the tip  52  of each panel  44 , is the top of a vertical lever  84 , there being one lever  84  located on each side of the body  2  of the hammer and which is associated with a corresponding panel  44 . The pivot mechanism for each lever  84  comprises a horizontal axle  86  rigidly attached to the lever  84  and which projects perpendicularly relative to the longitudinal axis of the vertical lever  84  into a hole  88  formed through the lower side of the tip  54  of the panel. The lower end of each lever  84  is rigidly connected to an end of a bar  96 , one lever being connected to one end of the bar  96 , the other lever being connected to the other end. The bar  96  traverses the width of the body  2  and is pivotally mounted about its longitudinal axis on the body  2 . Thus pivotal movement of one lever  84  about the longitudinal axis of the bar  96  results in a corresponding pivotal movement of the other lever. The levers  84  project in a direction from the ends of the bar  96  which is parallel to each other. The purpose of the two levers and bar is to ensure that the two panels  44  move in a forward or rearward direction in unison and that there is no twisting movement about a vertical axis which would be created if the panels  44  could move forwardly or rearwardly independently of the other panel. 
     The size of the hole  88  in the lower side of the tips  52  of the panels  44  is slightly larger than the diameter of the axles  86  within them to accommodate the pivotal movement of the levers whilst the panels slide linearly on the pegs. 
     It should be noted that the holes  46  in the panels  44  of the second embodiment are elongate but serve no additional function that of the triangular holes  46  in the first embodiment. 
       FIGS. 5 and 6  shows a third embodiment of the present invention. Where the same features are present in the third embodiment which were present in the first, the same reference numbers have been used. The majority of the features present in the first embodiment are present in the third embodiment. The difference (described in more detail below) between the third embodiment and the first embodiment is that the grip portion  42  is attached to the panels  44  via two vibration dampening mechanisms  100 ,  102 . 
     The top vibration dampening mechanism  100  comprises a rod  104  which projects from a top portion  106  of the central interconnecting section  110 , which interconnects the panels  44 , into a tubular recess  108  formed in the top section  112  of the grip portion  42  of the handle  8 . A spring  114  is sandwiched between the top portion  106  and the top section  112 , which biases the grip  42  away from the panels. The rod  104  can slide in the direction of Arrow G, in and out of the recess  108 . The spring  114  limits the amount of travel of the rod in and out of the recess  108 . The spring  114  damps the vibrations in the direction of Arrow G, and thus reduces the amount of vibration transferred from the central interconnection section  110  to the top of the grip portion  42  of the handle. 
     The bottom vibration dampening mechanism  102  also comprises a rod  116  which projects from a bottom portion  118  of the central interconnecting section  110 , which interconnects the panels  44 , into a tubular recess  120  formed in the bottom section  122  of the grip portion  42  of the handle  8 . A spring  124  is sandwiched between the bottom portion  118  and the bottom section  122 , which biases the grip away from the panels. The rod  116  can slide in the direction of Arrow H, in and out of the recess  120 . The spring  124  limits the amount of travel of the rod  116  in and out of the recess  120 . The spring  124  damps the vibrations in the direction of Arrow H, and thus reduces the amount of vibration transferred from the central interconnection section  110  to the bottom of the grip portion  42  of the handle. 
     The two vibration dampening mechanism provide linear vibration dampening to the grip portion  44  of the handle in a generally horizontal direction (Arrows G and H) whilst the spring  58  provides rotational vibrational dampening of the handle  8 .