Post driver

Abstract

A post driver comprising a vertical support strut (12) and a weight (14,104) vertically slideably mounted thereon, and operable such that the weight (14,104) can be raised vertically and released to fall vertically under gravity to collide with the top surface of a post positioned vertically thereunder; wherein the weight (14,104) comprises a primary weight (16,216) and a secondary weight (18,218) vertically aligned with the primary weight (16,216), and wherein the secondary weight (18,218) is vertically moveable relative to the primary weight (16,216), such that the secondary weight (18,218) can adopt a relative position between an uppermost relative vertical position and a lowermost relative vertical position, and the secondary weight (18,218) is biased towards its uppermost relative vertical position, but can move towards its lowermost position during a collision of the weight (14,104) with a post, as its momentum overcomes the resistance of the bias.

Description

[0001] POST DRIVER

[0002] Technical Field

[0003] The present invention relates to a pile driver comprising a vertical support strut and a pile vertically slideably mounted thereon, particularly but not exclusively for use in driving wooden posts into the ground.

[0004] Background and Prior Art

[0005] Pile drivers are devices that are used for the driving of a vertical post, beam or rod vertically downwards into a supporting surface, such as the surface of the earth, and are well-known. They operate by lifting a weight, or pile, followed by releasing the pile to fall under gravity to collide with and drive the post, beam or rod into the earth. In general a plurality of such collisions are necessary to achieve the required depth of driving of the post, beam or rod into the earth.

[0006] Pile drivers come in a range of sizes, depending on the type of application. For large-scale construction operations, specialised equipment is available, typically for driving metal posts, beams or rods. However, for smaller-scale operations, such as driving fence posts, which may be made of more fragile material, such as wood, the equipment available is rather simplistic. Essentially, such known pile drives for small scale operation involve a vertical supporting shaft, with a pile slideably attached, which can be raised and dropped onto a post.

[0007] However, difficulties can arise with driving such wooden posts, for example, the forces required to effectively drive them into the earth can exceed the yield strength of the post material itself, resulting in damage being caused to the upper region of the post. Using lighter weights, that do not cause such damage may be too slow for the effective driving of posts, which can be a significant consideration if a large number of such posts are required to be driven into the ground. Further improvements in this area would therefore be useful.

[0008] Brief Description of the Invention

[0009] In a first aspect, the invention relates to a pile driver comprising a vertical support strut and a pile vertically slideably mounted thereon, and operable such that the pile can be raised vertically and released to fall vertically under gravity to collide with the top surface of a post positioned vertically thereunder; wherein the pile comprises a primary pile and a secondary pile vertically aligned with the primary pile, and wherein the secondary pile is vertically moveable relative to the primary pile, such that the secondary pile can adopt a relative position between an uppermost relative vertical position and a lowermost relative vertical position, and the secondary pile is biased towards its uppermost relative vertical position, but can move towards its lowermost position during a collision of the pile with a post, as its momentum overcomes the resistance of the bias.

[0010] Such an arrangement has been found to be particularly effective at driving wooden posts into the ground, as the forces applied to the top surface of the post during the collision are spread out over time, due to the moveable secondary pile. This results in a more effective driving of the post into the ground without damaging the post.

[0011] The vertical support strut is typically made of metal and may, for example, be of an I-beam or box-section construction.

[0012] Preferably the ratio of the weight of the primary pile to the weight of the secondary pile is from 1.5:1 to 4:1.

[0013] Preferably the primary pile weighs from 100 to 500kg. Preferably the secondary pile weighs from 50 to 250kg. The secondary pile may sit above the primary pile, however preferably the primary pile comprises a cavity, and the secondary pile is contained within the cavity. The cavity may be empty or could be filled with a fluid, such as an oil.

[0014] Preferably the primary pile is vertically slideable within a pile housing. In such an arrangement the pile housing may remain stationary relative to the vertical support strut during movement of the pile. Such an arrangement ensures that the moving pile is safely contained within the housing, reducing the risk of accident occurring.

[0015] Conveniently, the biasing of the secondary pile towards its uppermost relative vertical position is achieved by use of a spring. Conveniently this can take the form of a spring being positioned between vertically beneath the secondary pile.

[0016] In one embodiment, the pile is raised vertically by the action of a cam positioned beneath the pile. Alternative methods of raising the pile vertically include a lifting cable.

[0017] Although the primary pile can simply fall under the action of gravity alone, in a preferred embodiment, its vertical descent can be assisted by the action of a spring, biasing the primary pile towards its lowermost position. This embodiment is particularly applicable when the pile is contained within a pile housing, as the spring can be conveniently located within the pile housing so as to act on the pile as needed.

[0018] The present invention is particularly suitable for small-scale applications, especially where a number of posts are desired to be driven into the ground. It is therefore convenient that the vertical support strut is mounted onto the rear of a tractor. This enables the pile driver to be easily moved from one post to the next.

[0019] Thus, in a second aspect, the invention relates to a method of driving a wooden post into the ground by use of a pile driver as described herein, wherein during the collision with the post the secondary pile moves from its uppermost relative vertical position to its lowermost relative vertical position.

[0020] In particular, the method involves the use of a mobile pile driver and the driving of a plurality of wooden posts into the ground.

[0021] Preferably the pile can drive the wooden post into the ground within a time period of 10 minutes or less.

[0022] The invention will now be illustrated, by way of example, and with reference to the following figures, in which:

[0023] Figure 1 a is a top view of a pile driver according to the present invention.

[0024] Figure 1 b is a side sectional view of the pile driver shown in figure 1 a.

[0025] Figure 2 is an image of the pile driver in use driving a wooden post into the ground.

[0026] Figure 3 is a sectional view through another pile driver according to the present invention with the pile in its uppermost position ready to be released under gravity.

[0027] Figure 4 is a sectional view through the pile shown in figure 3 with the pile in colliding with a post.

[0028] Turning to the figures, figures 1 a and 1 b show a pile driver 10 that comprises a vertical support strut 12 and a pile 14 vertically slideably mounted thereon, in the direction of arrow 15. The pile 14 comprises a primary pile 16 that is attached to the vertical support strut 12 and is moveable vertically thereon, and has a hollow cavity. Within the hollow cavity is located a secondary pile 18. Secondary pile 18 rests on a spring 20, that acts to bias the secondary pile to an uppermost position relative to the primary pile 16.

[0029] In use, the primary pile 16 is raised by pulling on attachment linkage 22, e.g. by a pulley system or rope or chain that may be hydraulically operated, once at the desired height, the pile 14 is then released to descend under gravity to collide with the top surface of a post, e.g. a wooden post. The momentum of the primary pile is then transferred to the post, and so is driven into the ground. Simultaneously, the secondary pile 18 moves relative to the primary pile 16 towards its lowermost relative vertical position. This adds to the momentum transferred to the post, but over a longer period of time. Thus, the post is driven effectively without a high peak force being applied which could overcome the material strength of the past, causing damage thereto.

[0030] Figure 2 shows a pile driver 100 according to the present invention in use and mounted onto the rear of a tractor 110. The pile driver 100 comprises a vertical support strut 102 and a pile 104 in the process of driving a wooden post 106 into the ground. The pile driver 100 comprises a pulley arrangement 112 which uses a rope 114 to raise the pile 104 by means of a hydraulic piston 116 powered by the tractor 110. The pile is similar in design to that shown in figures 1 a and 1 b.

[0031] The post 106 is effectively driven into the ground without damage being caused to it, which enables the tractor 110 to move on to enable a plurality of similar posts to be driven into the ground in an effective timeframe.

[0032] Figure 3 shows another pile driver 200 according to the present invention that comprises a pile housing 212 having a hollow cavity with internal lugs 217, within which is located a pile comprising a primary pile 216. The primary pile 216 is moveable vertically within the pile housing 212, and is biased to a lowermost position by a primary spring 219. The primary pile 216 also has a hollow cavity, within which is located a secondary pile 218. Secondary pile 218 rests on a secondary spring 220, that acts to bias the secondary pile to an uppermost position relative to the primary pile 216.

[0033] Attached to the exterior of the vertical support strut 212 is a drive motor 222 that is vertically moveable on a vertical support strut (not shown) and is operable to rotate a cam 224.

[0034] In use, drive motor 222 is moved vertically on the vertical support strut (not shown) until the pile housing 212 is in contact with the post 206. The cam 224 is then rotated by the action of the drive motor 222, which acts to raise the primary pile 216 within the pile housing 212 against the action of the spring 219, until the primary pile reaches its uppermost position relative to the pile housing 212, as shown in figure 3.

[0035] As the cam 224 continues to rotate the primary pile 216 reaches a point where it is no longer supported from below by the cam 224. This triggers the downwards descent of the primary pile 216 to fall vertically under gravity which is assisted by the action of spring 219. During this downwards phase the secondary pile 218 remains in its uppermost position relative to the primary pile 216 as shown in figure 3.

[0036] Eventually the primary pile 216 collides with the internal lugs 217 of the pile housing, and thereby also collides with the top surface of the post 206 positioned vertically thereunder. At the moment of collision with the lugs 217, the secondary pile 218 begins to move downwards from its uppermost position towards its lowermost position during the collision of the primary pile with the post, as its momentum overcomes the resistance of the spring 220. As the secondary pile 218 reaches its lowermost position, as shown in figure 4, further momentum is transferred to the pile housing 212 and therefore to the post 206. This adds to the momentum transferred to the post, but over a longer period of time. Thus, the post 206 is driven effectively without a high peak force being applied which could overcome the material strength of the post 206, causing damage thereto.

Claims

Claims1. A pile driver comprising a vertical support strut and a pile vertically slideably mounted thereon, and operable such that the pile can be raised vertically and released to fall vertically under gravity to collide with the top surface of a post positioned vertically thereunder; wherein the pile comprises a primary pile and a secondary pile vertically aligned with the primary pile, and wherein the secondary pile is vertically moveable relative to the primary pile, such that the secondary pile can adopt a relative position between an uppermost relative vertical position and a lowermost relative vertical position, and the secondary pile is biased towards its uppermost relative vertical position, but can move towards its lowermost position during a collision of the pile with a post, as its momentum overcomes the resistance of the bias.

2. A pile driver according to any one of the preceding claims, wherein the ratio of the weight of the primary pile to the weight of the secondary pile is from 1.5:1 to 4:1.

3. A pile driver according to any one of the preceding claims, wherein the primary pile weighs from 100 to 500kg.

4. A pile driver according to any one of the preceding claims, wherein the secondary pile weighs from 50 to 250kg.

5. A pile driver according to any one of the preceding claims, wherein the primary pile comprises a cavity, and the secondary pile is contained within the cavity.

6. A pile driver according to any one of the preceding claims, wherein the primary pile is vertically slideable within a pile housing.

7. A pile driver according to any one of the preceding claims, wherein the secondary pile is biased towards its uppermost relative vertical position by a spring.

8. A pile driver according to any one of the preceding claims, wherein the pile is raised vertically by the action of a cam positioned beneath the pile.

9. A pile driver according to any one of the preceding claims, wherein the primary pile is biased towards its lowermost position by a spring.

10. A pile driver according to any one of the preceding claims, wherein the vertical support strut is mounted onto the rear of a tractor.11 . A method of driving a wooden post into the ground by use of a pile driver according to any one of the preceding claims, wherein during the collision with the post the secondary pile moves from its uppermost relative vertical position to its lowermost relative vertical position.

12. A method according to claim 11 , wherein the wooden post is driven into the ground within a time period of 10 minutes or less without damaging the top of the post.

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