GB2271978A

GB2271978A - Fence post extractor

Info

Publication number: GB2271978A
Application number: GB9222663A
Authority: GB
Inventors: Richard Frederic Stannard; Alastair Forster Smith; John Rogers
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-10-28
Filing date: 1992-10-28
Publication date: 1994-05-04
Also published as: GB9222663D0

Abstract

A fence post extractor includes a main frame supported on front and rear feet (3 and 4). Pivotally attached to the main frame near one of its ends is a lifting frame comprising two lifting arms (2) of generally arcuate shape. Resting on the apex of the lifting arms is a clamping means (9) for clamping around a fence post to be extracted. The clamping means (9) is free to slide along the lifting arms. The front ends of the lifting arms (2) furthest from their attachment to the main frame, are rotatably attached to a lifting ram. Actuation of the ram lifts the lifting arms (2) and consequently the clamping means (9), causing the fence post to be raised and extracted from the ground. <IMAGE>

Description

TITLE: Fence Post Extractor DESCRIPTION The invention relates to apparatus for removing fence posts or poles from the ground.

Background of the Invention The removal of fence posts from ground in which they may have been embedded for many years is often difficult. One traditional method of removal involves the attachment of the post by ropes or chains to a tractor or other powerful vehicle so that it can be hauled from the ground by the movement of the vehicle. This is subject to a number of limitations. Access is often difficult, especially when the post is surrounded by uneven ground or ground that it is unacceptable to drive over. The force that the tractor is able to apply is limited by the attachment between the post and the ropes or chains, and it is often difficult to ensure that this attachment is sufficiently strong.

Another difficulty is that unless the tractor is provided with means for establishing a substantially vertical lift on the post, energy is expended in dragging the post out of the ground in a generally horizontal direction. A much higher force must be applied to the post than if the lift were vertical, and the subsequent removal of the post will cause more damage to the surrounding area. An additional limitation is the often prohibitive cost of hiring a tractor.

Another traditional method of post removal involves the digging out of the post by hand. This is obviously unsatisfactory from the point of view of time and labour, and may be impossible if the base of the post is inaccessible or the ground particularly hard. An object of the present invention is to provide a fence post extractor that eliminates the above difficulties, and is suitable for one-person operation.

Description of the Invention The invention provides a post extractor comprising a pair of feet for engaging the ground at opposite sides of a post to be extracted, a main frame extending between the feet, a lifting frame carrying a clamping mechanism for gripping the post to be extracted, and a hydraulic mechanism for raising the clamping mechanism on the lifting frame relative to the main frame.

The apparatus may be made relatively small and can be positioned around the majority of posts without causing damage to the surrounding area. It may also be made sufficiently light to be portable so that, in the event of the post being in an extremely awkward or inaccessible location, the extractor may be lifted and manoeuvered into place Preferably the main frame is designed to rise clear of the ground between the feet, to straddle any disturbed ground or overgrown vegetation that may surround the post to be lifted, or to straddle any concrete post foundations raised during lifting.

In certain circumstances the original post may have broken or been removed, leaving only a broken stump or foundations to be extracted from the ground. In cases such as these, where there is no post at an appropriate height to be gripped by the clamping mechanism, an auger may be driven into the foundations so that it effectively becomes the post referred to in the specification. The raising of this auger then causes the stump or foundations to be lifted out of the ground.

Preferably the lifting frame is pivotally connected to the main frame over one of the feet and is connected to the hydraulic mechanism, which may be a single lifting ram, over or generally over the other of the feet. The resulting pivotal movement of the lifting frame would not of itself provide a true linear vertical lift of the post by the clamping mechanism, and there is therefore preferably a tolerance of movement in the mounting of the clamping mechanism on the lifting frame. For example, the lifting frame may comprise two lifting arms one on each side of the post to be lifted, and each lifting arm may have a convex curved top face at least in a working zone supporting the clamping mechanism. The clamping mechanism then sits on the lifting arms, and can rock or slide over the curved top faces as the lifting frame is lifted pivotally about its pivotal connection.In this way the lift is always vertical, or at least always in a direction longitudinally of the post.

Preferably one or both of the feet are removable for ease of manoeuvering the extractor into position. For example, if the lifting frame comprises two lifting arms as described above, they may be separated from one another at their ends pivotally connected to the main frame, and the main frame and lifting frame may then be pushed around rather than lifted over the post to be extracted. Also the feet may accommodate a degree of pivotal movement relative to the main frame so as to take up any unevenness in the ground around the post without affecting the stability of the frame.

The clamping means preferably consists of two jaws, each shaped in a right angle, which are moved together with a handle to grip the post. The right angled shape of the jaws which are advantageously hard faced and serrated ensures that at least 4 points of contact with the post are achieved regardless of its shape. The jaws may in one variation of the invention be mounted on a selfacting cam which translates a vertical lifting force into a force with a component acting to increase the pressure between the jaws and the post, so that the grip on the post tightens as the upward force is applied.

Where stumps or foundations are being removed by the use of an auger, the auger may include a horizontal cross piece to aid its lifting. In this case it may be advisable to leave the clamping means relatively loose, and to rely on the upward force exerted on the cross piece by the top of the clamping means to raise the auger and hence the stump or foundation.

In the above described embodiment in which the clamping means sits on curved top faces of the lifting arms, the clamping means may be positioned around the post so that its outer edges rest on the apices of the curved lifting arms, the clamping means thereby bridging the gap between the arms. A smooth hardened inverted shelf on the bottom of each outer edge of the clamping means rests on a hardened section on the upper edge of the neighbouring lifting arm. This arrangement ensures that the clamping means is free to rock or slide over the curved top faces of the lifting arms as described previously.

Drawing The sole Figure of the drawing is a perspective view of a post extractor according to the invention.

A main frame consists of two parallel arcuate frame members 1, each comprising a main portion 16 and a front leg 15. The main portions of the two frame members are spaced apart to fit around a fence post, but the front legs are positioned closer together to reduce the size and weight of the apparatus.

Pivotably attached to and situated just internally of the frame members 1 are two lifting arms 2 of a lifting frame. Each lifting arm 2 is pivotally attached to its associated frame member 1 by a pivot pin 13, near the back of the apparatus. The lifting arms 2 are arc shaped and prior to lifting are enclosed neatly between the frame members 1. Their shape differs from the frame members 1 in that they do not extend right to the ground at the front of the apparatus.

The front ends of the lifting arms, furthest from the pivot pins 13, are rotatably attached to and joined together by a lifting bar 6. This in turn is attached to the top of a hydraulic ram 8, the bottom of which is mounted on a mounting bar 5. The mounting bar 5 is pivotably attached between the bottoms of the two front legs 15. The hydraulic ram 8 is activated by a hand or foot pump to raise the lifting bar 6 and force the lifting arms 2 to pivot about pivot pins 13.

On the apex of the lifting arms 2 rests clamping means 9.

The clamping means 9 includes a hardened, smooth inverted shelf 12 at each outer periphery, which contacts a hardened smooth section 11 on the top of each lifting arm 2. The clamping means 9 is not fixed to the lifting arms 2, but is free to slide along the arms, guided by its smooth shelves 12. The clamping means 9 consists of two jaws 10, each shaped as a right angle, which open and close in a direction parallel to the lifting arms 2.. The jaws are hard faced and serrated, and may be arranged on a self acting cam such that the grip on the fence post grows stronger as it is lifted. A handle 17 acting on an eccentric cam 18 is used to bring the jaws together, thereby clamping them around the fence post.

At the base of the front legs 15 is a stabilising front foot 3, consisting of a box portion and an angled support member 7. The angled support member 7 is slotted into a notch 14 in the base of each front leg 15, to locate the foot firmly underneath the frame. A rear foot 4 fits into similar notches in the bases of the frame members 1.

Activation of a hand or foot pump causes the hydraulic ram to extend, thereby forcing the lifting arms 2 to pivot about their pivot pins 13 near the rear foot 4 of the apparatus. The position of the clamping means 9 on the apex of the arcuate lifting arms 2 ensures that a vertical force is applied to the fence post via the clamped jaws 10. As the post rises from the ground, the pivoting of the lifting arms 2 shifts their centres slightly towards the rear of the apparatus. However, because of the shape of the arms, the apex of the lifting arms 2 remains substantially adjacent to the fence post.

The clamping means, being free to slide along the lifting arms 2, remain at this point, and the force on the post continues to be vertical. Similarly, even if the apparatus rests on sloping ground, with the feet 3 and 4 positioned at differing heights, the shape of the arms 2 ensures that a vertical force is always applied and the operation of the post extractor is not affected.

The lifting force applied may be up to five tons, enough to remove fence posts in all but exceptional circumstances.

Claims

CLAIMS:

1. A post extractor comprising a pair of feet for engaging the ground at opposite sides of a post to be extracted, a main frame extending between the feet, a lifting frame carrying a clamping mechanism for gripping the post to be extracted, and a hydraulic mechanism for raising the clamping mechanism on the lifting frame relative to the main frame.

2. A post extractor according to claim 1 wherein the lifting frame is pivotally attached to the main frame.

3. A post extractor according to claim 2 wherein the pivotal attachment is generally over one of the feet, and the hydraulic mechanism acts on the lifting frame at a point generally over the other foot.

4. A post extractor according to claim 3 wherein the lifting frame has a convex curved upper section extending over at least a portion of its length.

5. A post extractor according to claim 4 wherein the clamping means rests on the convex curved upper section of the lifting frame and is free to slide along the lifting frame.

6. A post extractor according to any preceding claim wherein the clamping means includes two right angle shaped jaws.

7. A post extractor according to any preceding claim wherein the clamping means is arranged on a self acting cam which translates a vertical lifting force on the clamping mechanism into a force with a component acting to increase the clamping pressure between the jaws and a post to be lifted.

8. A post extractor according to any preceding claim wherein at least one foot is detachable.

9. A post extractor substantially as described herein with reference to the drawing.