Shock absorber arrangements for use in fastener driving apparatus

Abstract

 57 A piston driver (17,18) is arrested by a shock absorber element (15) shaped and mounted so that it distorts primarily by deflecting and/or bending rather than by compression.
The advantage is thus achieved that the amount of heat generated in the element (15) is reduced and its service life increased.

Description

[0001] This invention relates inter alia to shock absorber arrangements for use in fastener driving apparatus.

[0002] Tools used for driving fasteners into a workpiece in a single blow may use a piston and a driver, attached thereto, which travel at a very high velocity. As the piston approaches the end of a cylinder it must come to an abrupt stop. The material composing the workpiece and the size of the fastener may help slow the piston but in many cases an additional means must be provided to prevent the piston and driver from striking metallic portions of the tool body.

[0003] If the piston strikes the body, severe damage may occur to both parts. To prevent this damage, most previously built tools have a shock absorber to absorb the energy created by the moving piston. A deformable element is inserted in the tool near the base of the cylinder in such a manner as to have the underside of the piston strike this material instead of the metallic body. There are some tools that have the element attached to the underside of the piston and carried by the piston during the stroke and some tools have a combination thereof.

[0004] In designing the shock absorber, two major problems must be overcome. First it must absorb most of the energy from the moving piston without transferring it onto the body or the shock absorber will be of little use. Secondly, the shock absorber must be able to withstand repeated cycles at a high rate without tearing apart in a short time. The internal heat due to compression builds up during rapidly repeated cycles and causes accelerated deterioration of the material of the element. An element that must be replaced frequently is both costly and time consuming. The same is true with an element that allows a portion of the body to fail and need replacing.

[0005] An object of the present invention is to provide a shock absorber arrangement for fastener driving apparatus that does not transfer a large portion of the shock to the body of the apparatus yet does not retain much heat created by compression of the shock absorber.

[0006] Another object of the present invention is to provide a shock absorber arrangement which reduces internal heat buildup during repeated cycles.

[0007] Another object of the invention is to provide a shock absorber arrangement in which the UFE of the shock absorber is extended when used in rapid cycle operations.

[0008] The objects have surprisingly been achieved by a shock absorber arrangement as defined by the appended claims.

[0009] According to one aspect of the invention, there is provided a shock absorber arrangement for fastener driving apparatus comprising a fastener driving member mounted for reciprocating movement in a housing and a shock absorber element disposed in said housing to arrest said driving member at a predetermined point of said movement characterised in that said element is so shaped and is mounted in such manner that when arresting said driving member said element distorts primarily by bending and/or deflecting.

[0010] According to another aspect of the invention, there is provided fastener driving apparatus characterised by said shock absorber arrangement.

[0011] For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

Figure 1 is a partial cross-sectional view of a fastener driving tool with a shock absorber according to the present invention;

Figure 2 is similar to Figure 1 with a piston and driver in downward position;

Figure 3 is a detail view of the shock absorber as it is contacted by the piston;

Figure 4 is a detail view as the shock absorber deflects; and

Figure 5 shows dimensional relationships of the shock absorber.

[0012] Referring now to Figure 1, a shock absorber 15 is disposed within a pneumatic fastener driving apparatus shown generally as 16. As in the case of most tools used to drive fasteners into a workpiece with a single blow, a driver 17 is attached to a piston 18 which is powered downward by compressed air applied to the upper side thereof, through a suitable valve means. Although the actuation of the value means has no relation to the present invention except to provide a rapid downward movement of the piston, a typical example is described in British Patent No. 1,087,183 in the name of Umberto Monacelli.

[0013] The fasteners shown in the illustrations are nails assembled as a strip although staples, pins, tacks and the like could be used depending on the particular tool involved. The leading fastener 20 of the assembly is moved into a driving throat 21 by a pusher means (not shown) after each cycle of the tool. The driving throat 21 is disposed within a portion 22 of the tool body 16 and is substantially on the same axis as the piston 18 and the cylinder 23. The driving throat 21 and driver 17 are illustrated as being circular but of course could be rectangular or of other shape depending on the fastener being utilized.

[0014] A typical operating cycle will now be described referring to Figure 1 and Figure 2. The tool is positioned against a workpiece and a trigger is actuated to start the cycle. A power valve means opens allowing compressed air to reach the top of the cylinder 22 above the piston 18. The piston 18 and driver 17 attached thereto start a rapid downward movement. The end of the driver 17 contacts the fastener 20 and drives it downward through the driving throat 21. The fastener 20 is separated from the rest of the fastener assembly as it moves towards the- workpiece.

[0015] As the fastener 20 enters the workpiece, the driver l7 and piston 18 decelerate due to the resistance to the fastener 20 entering the workpiece. At the end of the driving stroke, the underside of the piston 18 strikes the top portion 24 of the shock absorber 15. Depending on the resistance of the workpiece and the energy of the compressed air, the force the shock absorber 15 must withstand will vary. The greatest shock of course is when the fastener has not entered into the driving throat 21 due to a jam, or the tool has run out of fasteners and the shock absorber must withstand the full force of the piston.

[0016] When the piston is at the end of the stroke, holes 25 within the cylinder wall allows compressed air to enter chamber 26. The trigger is released, the power valve closes, compressed air above the piston 18 exhausts and the air within the chamber 26 can enter the area under the piston 18 through further holes 27.

[0017] The piston 18 and driver 17 return to. the upper rest position. As the end of the driver 17 clears the fastener assembly, the next fastener moves into the driving throat 21.

[0018] Referring now to Figures 3 and 4, the invention will be described in more detail as the piston 18 contacts the shock absorber 15 and it in turn stops the downward movement of the piston 18 and driver 17. The shock absorber 15 being generally circular in shape is supported on an external circumferential surface 28 by the cylinder 23 for the purpose of centrally positioning the shock absorber 15 within the tool. The shock absorber 15 is also supported vertically by its lower surface 29 resting on a conical surface 30 located in the base portion 22 of the tool 16. Although the conical surface 30 is deep, the surface 29 rests on only the outer edge thereof. The bottom surface 31 of the shock absorber 15, substantially transverse to the driver 17, is unsupported.

[0019] A void 32 is provided within the central portion of the shock absorber 15 to allow movement of the driver 17 therethrough. An upper surface 24 of the shock absorber 15 is contacted by the underside of the piston 18 during the downward stroke. The shape of the underside of the piston 18 is designed to provide a large external guiding surface 33 in contact with the cylinder 23 yet reduce the overall height of the tool below that which could be obtained with a solid flat piston. The external portion 34 of the shock absorber 15 is conical so as to match the outer portion 35 of the piston 18.

[0020] Figure 4 shows the shock absorber 15 in a deflected condition with the piston 18 having come to a full stop. As the force from the piston 18 is applied to the top surface 24, the shock absorber 15 deflects both inwardly and downwardly as opposed to pure direct compression as in previous tools of this nature. The present shock absorber may also compress slightly depending on the composition of the flexible material from which it is made.

[0021] The conical shape of the void 32 is to provide clearance for the p₀rtion _36 on the piston 18 and portion 37 of the piston base 22 as the void 32 changes shape during the inward deflection. The region 40 created between the conical surface 30 and the surface 31 is normally vacant in "at rest" position and provides space for the lower portion of the shock absorber 15 to enter during deflection without compression.

[0022] Referring now to Figure 5, the dimensional relationships can be seen that provide for deflection of the shock absorber 15 rather than compression when a force is applied to the top surface 25 thereof. The surface 29 that rests on a portion of conical surface 30 has a minor circumferential edge 38 where surface 29 meets surface 31. The top surface 24 has a minor circumferential edge 39 being the innermost part which is contacted by the underside of the piston 18 and having a diameter A less than diameter B of circumferential edge 38. Both surfaces 24 and 29 may also have major circumferential edges or may gradually merge into surfaces 34 and 28 respectively.

[0023] When a force is applied to edge 39, a resistant force reacts along edge 38. Since the force on edge 39 is radially inward of that on edge 38, and surface 31 is unsupported, the major portion of the shock absorber 15 will deflect downwardly and inwardly and will not undergo direct compression as would happen should surface 31 be allowed to rest against surface 30. Allowing the shock absorber 15 to compress causes internal heat that builds as the tool is cycled at high rate, which is the case in most applications. Heat causes changes in the properties of the material used to produce the shock absorber and the usefulness of the shock absorber diminishes. By having the shock absorber deflect, according to the present invention, although some compression may occur, the heat is reduced and the usefulness of the shock absorber is increased. The deflection action preferably. includes a degree of bending.

[0024] In an alternative embodiment, the surface 29 may extend transversely of the driver 17. The advantage of the invention is still achieved provided the minor circumferential edge 38 is larger than that of edge 39. The center void may also be a straight-through bore depending on the configuration of the piston 18 and body portion 20.

[0025] The shock absorber element may be made from any suitable material such as neoprene, Vulcolon or another synthetic plastics material. It may have a Durometer hardness of 75 to 80.

[0026] Instead of fixing the shock absorber element in the cylinder, it is of course equally possible to mount the same on the piston or other part of the movable fastener driving member.

[0027] The element may also have other configurations that that illustrated. It could for example be constructed as a hollow element deflectable into an internal cavity thereof, and it could be constituted by a plurality of separate pieces.

[0028] It is believed that the advantageous effect of increased service life (in some cases doubled) may be caused by the fact that by allowing deflection as well as compression some energy is returned to the piston during its return stroke instead of being converted into heat.

[0029] Although the preferred embodiments of the invention have been described in detail, other changes and modifications will be obvious to those skilled in the art and such changes or modifications are to be included within the scope of the invention as defined by the claims appended hereto.

Claims

1. A shock absorber arrangement for fastener driving apparatus comprising a fastener driving member (17,18) mounted for reciprocating movement in a housing and a shock absorber element (15) disposed in said housing to arrest said driving member at a predetermined point of said movement characterised in that said element (15) is so shaped and is mounted in such manner that when arresting said driving member said element distorts primarily by bending and/or deflecting.

2. An arrangement according to claim 1 wherein said element is generally annular.

3. An arrangement according to claim 2 wherein said member passes through said element.

4. An arrangement according to any one of the preceding claims wherein a clearance region (40) i3 provided adjacent a surface of said element opposed to a surface contacted by said member.

5. An arrangement according to claim 4 when dependent on claim 3 wherein said element has an annular contact zone (24) for contact with said member.

6. An arrangement according to claim 5 wherein said element has a further annular contact zone (29) which remains in contact with said housing.

7. An arrangement according to claim 6 wherein the inner diameter of said further annular contact zone (29) is greater than that of the other annular contact zone (24).

8. An arrangement according to claim 7 wherein said other contact zone (24) is a surface substantially normal to the direction of movement of said driving member.

9. An arrangement according to claim 8 wherein the outer diameter of said further contact zone (29) is closer than said inner diameter to said surface.

10. An arrangement according to any one of the preceding claims wherein said element has a lateral cylindrical surface portion (28) supported by a wall of said housing.

11. Fastener driving apparatus characterised by a shock absorber arrangement according to any one of the preceding claims.

12. For use in the arrangement of any one of the preceding claims, a shock absorber element (15) shaped so that it can be mounted in said arrangement so as to distort primarily by bending and/or deflecting when in use.

13. Pneumatic fastener driving apparatus including a body, a cylinder disposed in said body, a piston slidably disposed in said cylinder, a driver attached to said piston, means for moving said piston through a driving stroke and return stroke, a portion of said body defining a driving throat along the axis of said cylinder for guiding a fastener during said driving stroke, and resilient means for stopping said piston during said driving stroke, said resilient means comprising a cylindrical element having an axis extending substantially along the axis of said cylinder, a void along said axis through which said driver may pass, and a first surface to be supported by a portion of said body, a second surface substantially transverse of said axis to be contacted by said piston during said driving stroke, a minor circumferential edge of said first surface supported by said portion of body being of larger diameter than a minor circumferential edge of said second surface, whereby said cylindrical element flexes downward and toward said axis when said second surface is contacted by said piston.

Drawing