Abstract:
There is provided an hand-held pneumatic tool which has a body, a tool fitted to the lower end of the body and a handle at the upper end of the body. The handle is connected to the body by a resilient connection means which permits relative actual movement between the handle and the body.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the US national phase application of PCT International Application No. PCT/GB00/02079 filed Jun. 1, 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to hand held pneumatic tools of the type commonly used as demolition hammers. 
     BACKGROUND OF THE INVENTION 
     It is well known to provide a pneumatic tool for use as a demolition hammer, which tool comprises a body forming a cylinder and having a handle at an upper end and a tool receptacle at a lower end, a piston being reciprocable within the cylinder under the action of compressed air so as to strike the tool repetitively. The operator holds the tool with both hands, one hand being on the top handle and the other hand on the body of the tool. 
     Known tools of this nature impose a high degree of vibration upon the operator. In recent times there has been increasing concern as to the risk to health which such vibration poses, and current health and safety regulations in the United Kingdom are now planned which will try to reduce vibration levels to which operators of such tools may be exposed. There is accordingly a need for a tool of this type which imposes significantly lower vibration upon the operator&#39;s hands. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides a hand held pneumatic tool comprising a body which includes a cylinder, a tool holder at a lower end of the body, a handle at an upper end of the body, a piston reciprocable within the cylinder between a lower position in which it strikes a tool in the tool holder and an upper position, an inlet for receiving compressed air, and a first valve means interposed between the inlet and the cylinder so as to cause the piston to reciprocate within the cylinder; and in which the handle is connected to the body by a resilient connection means which permits relative axial movement between the handle and the body; and a hand grip is provided around the body at a location spaced from the handle, the hand grip being connected to the handle for movement therewith. 
     Preferably, the hand grip is formed integrally with a muffler through which exhaust air from the tool passes. 
     In one form of the invention, said first valve means is secured to the handle for movement therewith. In an alternative form, said first valve means is secured to the body. 
     Preferably, the resilient connection means comprises a plurality of guide posts (which may be provided by shouldered bolts) and spring means which may suitably comprise respective coil springs around one or more of said posts. 
     In a preferred embodiment, the tool further includes flow control means for varying the supply of compressed air from the inlet into the cylinder. 
     Preferably, said flow control means comprises a second valve means located between the inlet for receiving compressed air and the first valve means. 
     Preferably, said flow control means is adapted to vary the extent of opening of an air passage connecting said inlet to said first valve means. 
     Preferably, said flow control means is adapted to vary the compressed air supply in a plurality of discrete steps. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: 
     FIG. 1 is a cross sectional side view of a first embodiment of pneumatic tool according to the invention; 
     FIG. 2 is a plan view corresponding to FIG. 1; 
     FIG. 3 is a cross sectional end view of the same embodiment; 
     FIG. 4 is a cross sectional side view of a second embodiment; 
     FIG. 5 is a plan view corresponding to FIG. 4; 
     FIG. 6 is a cross sectional end view of the second embodiment; 
     FIG. 7 is a cross sectional end view of a preferred embodiment of the present invention; 
     FIG. 8 is a fragmentary sectional view on line A′—A′ of FIG. 7, illustrating a flow control valve; 
     FIG. 9A is a side view of a rod member forming party of the flow control value of FIG. 8; and 
     FIG. 9B is a development of a slot formed in the surface of the rod member of FIG.  9 A. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1-3, a first embodiment of the present invention is a pneumatic tool comprising a body  10  which provides a cylinder  12  in which a piston  14  reciprocates so as to strike the shank  16  of a cutting tool received in a tool holder  18  and secured by latch assembly  20 . 
     The upper end of the tool is provided with a handle  22  incorporating an inlet  24  for compressed air. A trigger  26  is used to enable or disable the admission of the compressed air by means of a valve rod  28  bearing on a valve ball  30 . 
     When the trigger  26  is operated, the compressed air supply is communicated to a valve assembly  32  which initially passes compressed air via a transfer passage  34  to the lower part of the cylinder  12  to move the piston  14  upwardly. As the piston  14  rises in the cylinder  12 , the air therein is compressed until it reaches a sufficient pressure to lift a valve member  36  of the valve assembly  32 , thereby cutting off the supply to the transfer passage  34  and communicating the compressed air supply to the upper part of the cylinder  12  and thus driving the piston downwardly to strike the upper end of the tool shank  16 . Exhaust air from this operation passes via an exhaust port  38  into a muffler shroud  40  and thence to the atmosphere via one or more apertures (not shown) in the muffler shroud  40 . 
     The tool as thus far described is largely conventional, but the tool of the present invention is provided with vibration isolating features as will now be described. 
     The valve assembly  32  is located within a recess of the handle  22 , and the latter is secured to the body  10  via four shouldered bolts  42  the lower ends of which are screw threaded in bores in the upper portion of the body  10 . One or more of the shouldered bolts  42  is surrounded by a coil spring  44 , thus permitting resilient relative axial movement between the handle  22  and the body  10 . 
     To accommodate such movement, the valve assembly  32  communicates with the transfer passage  34  via a short tube  46  which is fixed in the handle  22  and slidable within the transfer passage  34 . Also, the valve assembly  32  communicates with the upper part of the cylinder  12  via a tubular extension member  48  slidable within a seal  50  in the upper end of the cylinder  12 . 
     A second hand grip for the operator is provided by a cylindrical portion  52  of the muffler shroud  40  in a lower part of the tool. The portion  52  may be provided with rubber rings  53  bearing on the body  10 ; these act primarily as wear members and do not require to make a gas-tight seal. The opposite end  54  of the muffler shroud  40  is secured to the handle  22  by means of a plate  55  (which is fixed to the handle  22  by screws) and a clip surrounding the opposite end  54  of the muffler shroud  40 . A sealing plate  56  is glued to the handle  22  so as to close the access bores for the shouldered bolts  42  and thus prevent leakage of compressed air via those bores. 
     Turning to FIGS. 4-6, the second embodiment is similar to the embodiment already described and like parts are denoted by like reference numerals. In this embodiment however the valve assembly  32  and the compressed air inlet  24  are located in an upper portion of the body  10 . The valve rod  28  is connected to the compressed air inlet  24  by an extension rod  50 . 
     The body  10  is connected to the handle  22  by means of shouldered bolts  42  and coil springs  44  as before. In addition, however, a rod  62  welded to the top of the body  10  passes into a bore  64  of the handle  22  and mounts a nut  66  and washer  68  which bear on a rubber ring  60 . This feature is particularly designed for use in the situation where the operator pulls the tool backwards while continuing to operate it, with the rubber ring acting as an isolator during such reverse movement to minimize the transmission of vibration of the body  10  to the operator&#39;s hands. To accommodate such use, a clearance  70  is provided under the head of each bolt  42 . As an alternative, or in addition, rubber buffers could be provided under the bolt heads. 
     FIG. 7 shows a preferred embodiment of the present invention. This is substantially similar to the embodiment of FIGS. 1 to  3 , except as discussed below. 
     The embodiment of FIG. 7 includes flow control means comprising a second valve  80  positioned between the inlet for compressed air  24  and the first valve assembly  32 . The second valve  80  is used to control the flow of compressed air to the first valve assembly  32 . 
     The degree of vibration transferred from the tool to the operator&#39;s hands varies with the hardness of the material being worked on. In the previous embodiments, a greater degree of vibration will be transferred to the operator&#39;s hands when relatively soft materials are being worked on than with relatively hard materials. It has been found that the degree of vibration can be controlled by varying the supply of compressed air to the tool. The flow control means  80  of this embodiment enables the supply of compressed air to the valve assembly  32  to be varied to suit the hardness of the material being worked on. 
     In practice, it has been found that optimum conditions exist for different materials for minimising the vibration transferred to the tool operator whilst ensuring that sufficient compressed air reaches the piston  14  of the tool to allow the tool to function properly, as follow: 
     Non-homogeneous sand valve approximately 25% open and “friable” materials such as coal 
     Limestone, soft rocks, valve approximately 50% open 
     heavy clay 
     Concrete Valve approximately 100% open. 
     The second valve means  80  can be of any type which allows the flow of air to the valve assembly  32  to be controlled. Preferably, the second valve means  80  can be set in a plurality of discrete positions to suit different materials, but could be continuously adjustable. The valve  80  should be lockable in the desired position so that its setting cannot be altered accidentally or by the action of the compressed air. 
     FIGS. 8 and 9 illustrate an embodiment of a suitable flow control valve  80 , comprising a generally cylindrical rod member  82  slidably located in a bore  84  which extends transversely to and intersects the air passage  86  connecting the air inlet  24  to the valve assembly. When the rod member  82  is positioned fully home in the bore  84 , as illustrated in FIG. 8, the rod member closes the air passage  86 , isolating the valve assembly  32  from the compressed air inlet  24 . By sliding the rod member out of the bore (towards the right hand side as seen in FIG.  8 ), the air passage may be opened partially or completely depending on the position of the rod member  82 , thereby controlling the supply of compressed air to the valve assembly  32 . 
     In this embodiment, the rod member  82  may be set in one of four discrete positions by means of a stepped slot  88  formed in the surface of the groove and extending around the circumference thereof, as illustrated in FIGS. 9A and 9B, which cooperates with a locking screw  90  which extends into the bore  84 . The rod member  82  may thus be set in one of the four positions defined by the slot  88  by rotating and advancing or retracting the rod member  82  in the bore  84 . As is best seen in FIG. 9B, the slot  88  defines four rotational positions  92 ,  94 ,  96  and  98  at 0°, 90°, 180° and 270°. Position  92  corresponds to the rod member  82  being fully home as seen in FIG. 8, closing the air passage  86 . Position  94  corresponds to a first partially retracted position of the rod member  82 , such that about 25% of the area of the air passage  86  is exposed (for soft materials). Position  96  corresponds to a second partially retracted position of the rod member  82 , such that about 50% of the area of the air passage  86  is exposed (for medium hardness materials). Position  98  corresponds to a fully retracted position of the rod member  82 , such that 100% of the area of the air passage  86  is exposed (for hard materials). 
     The rod may be manipulated by means of a handle member  100  and locked in the desired position by means of the screw  90 . 
     The illustrated flow control valve may be replaced by any equivalent flow control means providing either discrete or continuous adjustment of the compressed air supply to the valve assembly  32 . Similar flow control means could also be incorporated in the embodiment of FIGS. 4 to  6 . 
     Modifications to the foregoing may be made in the scope of the present invention.