IMPROVEMENTS IN PNEUMATIC POWERTOOLS

Abstract: A pneumatic power drill comprises a piston (13) reciprocal in a cylinder (12) defined within a cylindrical casing (11) of the tool. A bit (14) is actuable by the piston and means are provided by supplying air and pressure alternatively to opposite sides of the piston to reciprocate the piston in the cylinder. A handle (20) is slidably attached to the casing, resilient connection means being provided between the handle and the casing. The resilient connection means comprise a spring (46) and an air damper formed by compressed air filling a space around spring (46). The resilient connection means ensure that, in use, the vibration transmitted to the handle from the tool is substantially reduced.

Description: IMPROVEMENTS IN PNEUMATIC POWERTOOLS The invention relates to pneumatic power tools, particularly reciprocating pneumatic power tools of the type comprising a piston which reciprocates, in use, in a cylinder, means being provided to supply air under pressure alternately to opposite sides of the piston to cause the reciprocating motion. A tool or operating bit mounted in the power tool is acted on by the piston. Such a tool may, for example, be a chisel bit and a typical use of such a power tool is as a chipper in which the reciprocating motion of the piston causes the chisel bit to be hammered into a surface on which the tool is being used. Such pneumatic power tools are provided with a handle for a user of the tool and, in prior art devices, the handle is traditionally fixed rigidly to the cylinder or casing of the tool. This arrangement has a substantial disadvantage in that the vibration caused by the reciprocation of the piston in the cylinder is transmitted directly to the handle and thence to the hand and arm of a user of the tool. Significant periods of use of such a tool can cause a complaint known as vibration white finger, a symptom of which is the fingers of the user turning white and the long term effects of which can be very serious to the user. The present invention seeks to reduce this disadvantage of traditional reciprocating pneumatic power tools by providing such a tool in which the vibration transmitted to the handle is substantially reduced. The invention provides a pneumatic power tool comprising a piston reciprocable in a cylinder defined within a casing of the tool, a tool actuable by the piston, means for supplying air under pressure alternatively to opposite sides of the piston to reciprocate the piston in the cylinder and a handle slidably attached to the casing resilient connection means being provided between the handle and the casing whereby, in use, the vibration transmitted to the handle is substantiallly reduced, in which the resilient connection means includes an air damper arranged between the handle and the casing. The resilient connecting means preferably further comprises a spring located between the handle and the casing. A valve may be provided comprising a piston like valve member sliding in a cylindrical valve body, relative axial movement between the handle and" the casing causing the valve member to move between a first position in which a passage through or past the valve member allows a bleed of inlet air to be provided to the piston and cylinder arrangement and a second position in which a full flow of inlet air is provided to the piston and cylinder arrangement. The valve member may include a radial flange which is a close fit in the cylindrical valve member and in which the bleed is provided by a flat formed on the radial flange. The air damper is preferably provided by the valve member and valve body inlet air being provided to the interior of the valve body to act on the valve member. The tool may further comprise a sleeve extending around the piston and cylinder arrangement, the sleeve being resiliently mounted on the tool. The sleeve is preferably supported by a resilient mounting fixed to the casing and is coupled to a portion of the tool by a quick release coupling. Further features and advantages of the invention will be apparent from the following description, by way of example, of a preferred embodiment of a pneumatic power tool according to the invention, the description being read with reference to the accompanying drawings, in which: Figure 1 is a schematic section through a typlical prior art pneumatic power tool of the reciprocating piston type; Figure 2 is a longitudinal section through a pneumatic power tool according to the invention; Figure 3 is an enlarged scrap section through an inlet valve of the tool of Figure 2, showing the valve in a first position, and Figure 4 is a view i ilar to Figure 3 showing the valve in a second position. Figure 1 shows a reciprocating pneumatic power tool 10 which is a prior art chipper or hammer. The power tool 10 is typical of prior art tools of this type. Referring to Figure 1, the main components of the tool are a generally cylindrical casing 11 which defines therein a cylinder 12 in which a reciprocating piston 13 is slidably located. A tool or bit 14 is arranged co-axially with the piston 13 and extends through an end cap 15 of the tool which is screw-threadedly fixed to an end of casing 11. The tool includes a shoulder 17 and a portion of the tool to the left of the shoulder as viewed in Figure 1 is slidably located in a bush 18 located in the end of casing 11. A buffer 19 of resilient material located within the end cap 15 surrounds the tool 14 to the right of the shoulder 17 as viewed in Figure 1. A handle 20 of the power tool is fixed to the casing 11, as shown in Figure 1 by a screw-threaded connection. The handle 20 includes an inlet nipple 21 for compressed air and an inlet valve 22 which is spring urged into a normally closed position and is opened by a trigger 23 acting on an end of the valve and manually operated by a user of the tool. An end cap 25 closes off the end of the cylinder 12 remote from the tool 14 and is trapped between the casing 11 and handle 20. A valve and porting arrangement not shown in detail in Figure 1 but indicated generally by 16, 26 is arranged to provide compressed air alternately to opposite sides of the piston 13 to cause the piston to reciprocate in the cylinder. Compressed air is supplied to the valving arrangement 16 from inlet nipple 21 through passages 27 in the handle when the trigger 23 is operated to open the inlet valve 22. In use of the power tool 10 a user grips the handle 20 usually in his right hand and uses his left hand to steady the casing 11 of the tool and guide the bit 14. Operation of the trigger 23 causes compressed air to be supplied to the piston and reciprocate the piston which in turn, applies a hammering action to the bit 14 to drive the bit into a work piece. It will be appreciated that the connection between the handle 20 and casing 11 is rigid as shown in Figure 1. This, and the usual practice of positioning the user's free hand on the casing 11 causes all the vibration produced by the reciprocating action of the piston on the bit 14 to be transmitted to the hands of a user of the tool. This can cause severe discomfort to the user and can lead to a variety of vascular, nerve, skeletal and joint injuries including the condition known as vibration white finger. Turning now to Figures 2, 3 and 4, there is illustrated a pneumatic power tool 30 according to the present invention. A number of the components of the power tool 30 are essentially similar to those in the power tool 10 of Figure 1 and such like components are indicated by the same reference numerals as in Figure 1. These include a piston 13, sliding in a cylinder 12, the cylinder being formed in a generally cylindrical casing 11. A tool or bit 14 (only part of which is shown in Figure 2) is mounted co-axially with the piston 13 and extends through an end cap 15 of the power tool, the bit 14 being located in a bush 18 and resilient buffer 19. A handle 20 again includes an inlet nipple 21 and an inlet valve 22, urged by a spring 24 into a normally closed position and opened by trigger 23 which is manually operated and acts on an end of the valve 22. Passages 27 again allow compressed air supplied to the inlet nipple 21 to pass to the operative part of the power tool. The casing 11 has a generally cylindrical valve chest insert 29 which houses a reciprocating valve 31 and i located co-axially in an end of the cylinder remote fro the bit 14. The valve assembly is retained assembled in th cylinder end by an end cap 32. Inlet air to the power too flows around end cap 32 and via ports 33 and valve 31 int the cylinder 12 to urge the piston 13 to the left as viewe in Figure 2 and cause the piston to hammer the bit 14 Return reciprocation of the piston 13 is produced b compressed air supplied through passage 35 and port 36 t the left hand side of the piston as viewed in Figure 2 exhaust air passing through passages 37 and out through silencer 38 comprising silencing material located within retaining sleeve 39 located around a portion of the casin 11 and sealed thereto by 0-rings 34. The portin arrangement described above is essentially similar to th valve and porting arrangement 26 of Figure 1. In Figure 2, the casing 11 is not fixed directly t the handle 20 but is rather screw-threadedly connected a its end remote from tool bit 14 to an intermediate housin 40. Housing 40 is generally tubular including a central we 41 which retains end cap 32 assembled in the end o cylinder 12 and defines an air inlet passage 43 connectin with air inlet ports 33. Air inlet passage 43 in tur connects with a passage 44 extending through a tubula portion of the housing 40 projecting from the web 41 to th right as viewed in Figure 2. A valve housing 45 is slidabl connected to housing 40 by pins 47 located in slots 4 formed in the valve housing 45. A spring 46 is locate between the housings 40 and 45 to urge the housings apar to the position shown in Figure 2. The valve housing 45 ha a major cylindrical portion 49 in which the slots 48 ar formed and which portion 49 fits within a tubular portio 50 of handle 20. Resilient rubber rings 52, 53 are locate between valve housing 45 and the handle 20. A generally tubular handle extension 55 is scre threadedly fixed to the free end of handle 20 and acts a a lock nut retaining the handle 20 assembled with th housing 40 and casing 11. The assembly of handle 20 and handle extension 55 extends around the intermediate housing 40 and is located in position on a bush 56 made of low friction material such as nylon and a spacer 57 between which a spring 58 is located. Thus, it will be appreciated that the handle 20 is located on resilient mountings with respect to the casing 11 and intermediate housing 40 and is not rigidly fixed either to the casing 11 or intermediate housing 40. The leading part of the power tool 30 (the left hand section of casing 11 as viewed in Figure 2) and end cap 15 are located within a tubular cover or sleeve 60 of step cylindrical configuration which extends around the end cap 15 and casing 11. Cover 60 rests on a resilient mounting or bush 61 and is connected to handle extension 55 by pins 62 fixed to handle extension 55, which pins are located in slots 63 in the end portion of cover 60. The slots 63 are of similar shape to those found in electric light sockets so that, together with pins 62, they form a bayonet connection which is a quick release coupling between the cover 60 and handle extension 55. Thus, it will again be appreciated that the cover 60 is not rigidly fixed to the casing 11 but is resiliently mounted thereon. Reverting to the valve housing 45, this includes a generally tubular valve body portion 65 which extends into a hollow cavity 66 within the handle 20. A valve member 67 is slidably located within the valve body 65, a spring 68 being located between the right hand end of the valve body 67 (as viewed in Figure 2) and an end cap 69 fixed in the valve body 65, the spring urging the valve member 67 into the position shown in Figures 2 and 3. The left hand end of the valve body 67 abuts the tubular portion of intermediate housing 40, a seal 70 being interposed therebetween. The valve body 67 includes air inlet orifices 71 and a further air inlet orifice 72 is provided in the end cap 69. The valve body 67 (which is seen in better detail in Figures 3 and 4) includes a central passage 74 having radial air inlet holes 75 and being in connection with air inl passage 44, the seal 70 ensuring a substantially air tig connection between passages 74 and 44. The valve member includes radial flanges 77 78, the flange 77 including flat 79 which, in the rest possession of the valve viewed in Figures 2 and 3 provides a bleed of air throu inlet orifice 71 to holes 75 and thence to the air inlet passage It will be seen from Figure 2 that the tubul extension of housing 40 is a loose fit within valve housi 45 so that a lack of perfect concentricity, between t housings 40, 45 does not prevent the tubular extensi sealing on seal 70. In operation of the power tool 30, the componen start at rest in the position shown in Figure 2. A user the tool grasps the tool with one hand located around t handle 20 and the other supporting the cover 60. Initiall when the trigger 23 is pressed by the thumb of the hand the operator on the handle, air under pressure flo through inlet nipple 21, past valve 22 and through inl passages 27. The compressed air will then fill chamber and pass through orifice 72 to fill the space around spri 68 and act on the end of valve member 67. The flat allows a limited bleed of inlet air to flow throu passages 74, 44 and 43 to supply air to the cylinder 12. this position, the power tool is ticking over but the val member 67 prevents full supply of air to the cylinder 12 When a user then places the bit 14 against a wo piece and applies force generally axially to the power to through handle 20, it will be appreciated that the pinn connection between housing 40 and valve housing 49 allo the handle 20 to slide axially relative to the casing 1 It will also be appreciated that this sliding moveme causes the tubular extension of housing 40 to move val member 67 to the position shown in Figure 4 in which a fl of inlet air is allowed to pass the valve member 67 a flow through the inlet passages as described above to cau full reciprocating motion of piston 13 and hammer the b 14. Thus, it will be appreciated that valve member 67 prevents full reciprocating motion of the piston until the power tool 30 is in contact with the work piece and axial force is applied to the tool and it will be seen that this has advantages in safety. Furthermore the.angle of flat 79 ensures that as the valve member moves from its first rest position (Figure 3) to its second open position (Figure 4) the increase in supply of compressed air to the piston 13 is progressive. As the handle 20 slides axially relative to casing 11, the sliding movement is resisted by spring 46 and an air damper formed by the compressed air filling the space around spring 68. The spring force of spring 46 and the area of the valve member 67 forming the air damper are chosen so that, in use of the power tool 30 with a user applying typical axial force to handle 20, the pins 47 are in an intermediate position in the slots 48 so that the handle is supported relative to the casing 11 solely by the resilient mountings described above. As the handle 20 and cover 60 are supported solely by these resilient mountings it will be appreciated that the vibration transmitted to a user of the power tool will be very substantially reduced. In use of the power tool 30 when it is acting as a chipper and the bit 14 has a chisel blade, it is sometimes necessary to guide the bit 14. As the tool is guided, a torque may be applied to the casing 11. The pinned connection between housing 40 and valve housing 49 keys these two components together and torque may be transmitted from the handle to the casing 11 as the rubber rings 52 53 provide a very high friction contact with the handle 20 which allows the transmission of some torque to the casing 11, while absorbing torque vibration. The power tool 30 described above has a number of advantages over the prior art tool 10 illustrated in Figure 1. As described, the resilient mounting of the handle with respect of the casing of the power tool substantially reduces the vibration transmitted to a user of the tool. Furthermore, the fact that substantially less vibration i being transmitted to the handle allows the handle to b made from a much lighter material than has hitherto bee possible. For example, plastics or aluminium allo materials might be used for the handle 20. As also described above, the arrangement of valv member 67 prevents full reciprocating motion of the pisto 12 until the tool bit 14 is in contact with a work piece This prevents the bit 14 hammering against the buffer 1 and end.cap 15 of the power tool in an unloaded condition Again, this allows the end cap 15 to be made of a lighte material than hitherto. The invention is not limited to the preferre embodiment described above and various modifications may b made to the power tool 30 within the scope of the inventio as defined in the appended claims. For example, the pins 4 connecting housing 40 to valve housing 49 might be replace by rollers or other low friction connectors. Further, th bush 56 and spacer 57 may be of a suitable resilien material such as a rubber rather than nylon.

Claims: CLAIMS: 1. A pneumatic power tool comprising a piston reciprocable in a cylinder defined within a casing of the tool, a tool actuable by the piston, means for supplying air under pressure alternatively to opposite sides of the piston to reciprocate the piston in the cylinder and a handle slidably attached to the casing, resilient connection means being provided between the handle and the casing whereby, in use, the vibration transmitted to the handle is substantiallly reduced, in which the resilient connection means includes an air damper arranged between the handle and the casing. 2. A power tool as claimed in claim 1 in which the resilient connection means further comprises a spring located between the handle and the casing. 3. A power tool as claimed in claim 1 or claim 2 in which a valve is provided comprising a piston like valve member sliding in a cylindrical valve body, relative axial movement between the handle and the casing causing the valve member to move between a first position in which a passage through or past the valve member allows a bleed of inlet air to be provided to the piston and cylinder arrangement and a second position in which a full flow of inlet air is provided to the piston and cylinder arrangement. 4. A power tool as claimed in claim 3 in which the valve member includes a radial flange which is a close fit in the cylindrical valve member and in which the bleed is provided by a flat formed on the radial flange. 5. A power tool as claimed in claim 3 or claim 4 in which the air damper is provided by the valve member and valve body, inlet air being provided to the interior of the valve body to act on the valve member. 6. A power tool as claimed in any of the proceeding claims further comprising a sleeve extending around the piston and cylinder arrangement, the sleeve being resiliently mounted on the tool. 7. A power tool as claimed in claim 6 in which the sleeve is supported by a resilient mounting fixed to the casing and is coupled to a portion of the tool by a quick release coupling.

Inventors: HALL RAYMOND JOHN, HALL, RAYMOND, JOHN
Applicants: COMPAIR POWER TOOLS, HALL RAYMOND JOHN, COMPAIR POWER TOOLS LIMITED
Application year: 1993
Main classification: B25D17
IPC codes: B25D9, B25D17