It is usual to drive posts into the ground by means of mechanically operated systems, such as are used in piling for house foundations, but these are of necessity large and complex in construction. Systems for small scale use which do not necessitate mechanically operated means are known. These generally comprise a sleeve adapted to fit over the post provided at the top end with a cap so as substantially to close the sleeve and the sleeve is moved up and forced downwards manually. Driving posts with such apparatus is often an arduous process, specially with hard ground, and means are known for reducing the physical effort involved.

US-A-3856092 involves a weighting system, separate from the capped tube which is adapted to fit over the post. The weighting system is provided with stiff springs between the weight system and the capped tube, so that there is a resilient rebound effect, which reduces the force that has to be expended in lifting the apparatus. This has obvious disadvantages in tending to reduce the impact force of the cap.

There is still a need for a lightweight system which is easily portable, and which would permit the driving of posts in a simple manner with the minimum expenditure of energy.

The present invention provides a post driver apparatus, comprising a post sleeve capable of being fitted to an upper end of a post intended to be driven by the apparatus, the post sleeve having means for supporting an impact tube in which a weight is mounted for axial movement therein when the tube is aligned in a generally vertical attitude, the weight being capable of being lifted by a line which passes over a pulley located at an upper end of the tube. Preferably, the post sleeve carries one or more wedges, the wedges being supported by resilient means such that they will tend to grip a post of a predetermined diameter when this has been fitted in the sleeve.

The post sleeve may include an adapter section capable of supporting the said impact tube such that the post sleeve and impact tube will be retained on a common longitudinal axis. The post sleeve, at an end adjacent the said adaptor section, may support a bobbin capable of transmitting impact forces to a post when this is present in the sleeve.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a longitudinal section through a tube forming part of the system, Figure 2 is a view of the tube from above, Figure 3 is a view of a sleeve adapted to surround a post to be driven using the apparatus of Figure 1, Figure 4 is a longitudinal sectional view, showing on an enlarged scale a bobbin used in one embodiment of the invention, Figure 5 is a partial side view of an alternative construction using a lifting line which cooperates with a vee pulley, Figure 6 is a cross-sectional view taken on the line VI-VI of Figure 5, Figure 7 is a further embodiment showing a vee pulley connected to a drive motor, and, Figure 8 is a partial view from above of the Figure 7 embodiment.

Referring now to Figures 1 to 4 of the drawings, an impact tube 1 has within it a weight 2, adapted to be reciprocally moveable along the bore of the tube. The weight 2 is supported on a line 3 extending axially of the tube and over a pulley 4 jòurnalled within a pulley block 5 at the top of the tube. The free end of the line 3 remote from the weight 2 is provided with a number of grips 6 so that the weight 2 may conveniently be raised manually. Between the weight 2 and the pulley block 5 there is located a spring 8. The outside of the tube includes handles 7, so that it may be easily carried.

Figure 3 shows a sleeve 10 which is adapted to fit over a fence post and which is provided at its upper end with an adapter section 11 of larger internal diameter than the tube 1. The diameter is such as to form a slidable fit with the exterior lower end of tube 1.

In order to engage a post to be driven, two triangular wedges 12,13 are mounted within respective longitudinal slots 14 in the walls of the sleeve. The lower ends 15 of these wedges 13 are pivoted at the walls of the sleeve. Their upper ends 16 are urged into the interior of the sleeve, before fitting this on to the post, by elastic means formed by rubber rings 17, encircling the sleeve. When the sleeve is placed over a post to be driven, and moved longitudinally along the post, the upper ends of the wedges 13 will be forced radially outwards, and project out of the slots so that the sleeve may engage the post. The tube 1 is then placed within the adapter section 11.

Operation of the system according to the invention is quite simple. A downward pull on the free end of the line causes the weight 2 to be lifted compressing the spring 6. At an appropriate height, the free end of the line 3 is released, and the forces of gravity plus the spring cause the weight 2 to be moved downwards so as to impact upon the top of the post.

In one preferred embodiment of the invention, depicted in Figures 3 and 4, the impact of the weight 2 is not directly transmitted to the post, but is transmitted from the weight to the post by means of a bobbin 20. This bobbin has a cylindrical upper section 21, a cylindrical lower section 22 and an intermediate section 23. The upper, lower and intermediate sections are generally cylindrical, the diameter of the intermediate section 23 being less that that of the upper and lower sections 21 and 22.

This bobbin is retained by a section 24 at the top of the sleeve 10, this section 24 being circular and coaxial with the sleeve and having an internal diameter less than that of the upper and lower sections of the sleeve but greater than the diameter of the intermediate section 23 of the bobbin. In a manually portable version of the post driver, this clearance may be about two millimetres, but the exact clearance is of no significance except insofar as it should be sufficient to allow free movement of the bobbin. Section 24 is of shorter axial dimensions than the intermediate section of the bobbin so that the bobbin 20 is movable axially within the section 24. When a post is inserted into the sleeve 10, it pushes the bobbin 20 until the upper face of its lower section 22 contacts the lower face of section 24. Then, when the weight 2 impacts the upper face of bobbin 20, the force of the impact is transmitted to the post by the bobbin.

In an alternative embodiment, the bobbin 20 may be dispensed with, and the weight 2 will be provided with a lower portion which has a reduced diameter, adapted to pass through section 24 and impact directly on the top of the post.

The tube and sleeve are advantageously constructed of a rigid abrasion- resistant plastics material, such as an acrylonitrile butadiene styrene (ABS) or of material of comparable characteristics, which may if desired be reinforced with suitable fibres or fillers. The advantage of using a plastics material rather than a metal is that it can considerably reduce the weight of the apparatus and make it more readily portable. The tube and sleeve may, however, be constructed of metal or a suitable alloy, for example, duralumin (Registered Trade Mark). The metal may, if desired, be provided with a corrosion proofed surface, for instance, by anodizing.

An advantage of the invention is that the impact force is not transmitted back from the post to the post driver. The spring loaded wedges on the post sleeve allow movement and a dampening effect, which cushions the shock when the post is impacted. The bobbin also stops impact vibration being transmitted to the main machine. The tube and sleeve act as guides for the weight and post without the forces of impact being transmitted to them.

A prototype machine constructed for ready portability, has an impact tube 1 of length 5 feet (1.52m), an internal dimension of 5 ins (12. 7cm), an impact tube external dimension of 5.625 ins (14.29cm) and an impact tube weight of 11 lbs (5 kg).

The total weight of the machine is 35 lbs. (15.9 kg). The exact dimensions are not essential to the invention, and may be varied as desired.

The figures above show that the impact tube weighs less than one third of the total machine weight.

The post driver machine described and shown in Figures 1 to 4 of the drawings is a machine which is operated manually, that is, by pulling and releasing the line. One man can easily carry and operate this machine.

If it is desired to increase the power to be exerted on the top of a post to be driven, this can be done by providing an impact tube 1 of greater length, increasing the strength of the spring 8, or by increasing the mass of the weight 2.

This machine could easily be manufactured as a two man machine or a power operated machine. For example, a two man machine could be at least twice as heavy as the machine just described, that is, 70 lbs (31.8 kg) in weight. It could have two pulleys and two ropes allowing the potential to double the impact of the weight. The mass of the weight 2 could be increased. The compression rate of the spring 8 could be increased. The tube diameter and length of the tube could be increased. Tube internal diameters could vary from 2 ins to 10 ins (6.1 to 30. 5 cm). The mass of the weight could vary between 2 lbs and 55 lbs (0.9 and 25.0 kg). The force exerted by the fully compressed spring could possibly be increased as far as 300 lbs (136.2 kg).

The tube length could be between 2 feet and 10 feet (0.61 and 3. 05m).

These parameters should cover most practical applications for the post driver machine and hopefully any other use to which the machine may be put. Apparatus having the same weight and dimensions parameters as listed previously could also be used for one or two man operation.

A spike can be used to punch a pilot hole into hard ground. The dimensions of this spike can vary depending upon the size of post intended to be used, and could make the need to bore a pilot hole with an auger unnecessary.

The use of the apparatus according to the invention may be carried out safely since all moving parts are contained within the tube so that the risk of injury to an operator will be minimised.

The apparatus has been described with reference to manual operation. It could, however, if desired, be mechanized. For example, the pulley carrying the rope may be connected to a drive motor which would rotate the pulley. Rotation of the pulley would wind up the rope hence pulling the weight up the tube against the compression of the spring. At a certain point, that is, at the end of the stroke, the motor would either switch into reverse or be clutch operated to release the pulley and hence drop the weight. The motor could be a light-weight slow running motor of between 125 and 450 rpm and be operated by air, electricity or other power means.

Most sites would not have services provided to provide a convenient power source so alternative sources such as portable generators, compressors, etc may be employed.

A further alternative means of pulling the weight up the tube would be to use a double acting air cylinder. The air cylinder would be pressurised to pull on the rope which would lift the weight. The air supply would then be switched to the other end of the cylinder, and the weight would fall. A convenient size of air cylinder has a twelve inch (0.30m) stroke. The pulley will have a 4: 1 or 5: 1 gearing so that one stroke of such an air cylinder would lift four or five times that height.

In a further embodiment, Figure 5 shows a different lifting line and pulley construction where the original pulley has been replaced by a vee pulley 4 having the usual vee shape of profile at its periphery. Similarly, the lifting line has been replaced by a vee belt type of line 3 having a cross-sectional shape corresponding to the shape of the pulley periphery. In this embodiment, the pulley 4 is fixed to a shaft 26 which is supported in suitable openings in the walls of the impact tube. Figure 6 is a cross- sectional view taken on the line VI-VI of Figure 5.

In operation of this arrangement, when the pulley is positioned at the top of the impact tube, a user of the apparatus will pull down on the free end of the line 3 and this will cause the vee shaped cross-section of the line to enter the vee opening around the periphery of the pulley 4. When the line 3 is in this position, as depicted in Figure 6, a maximum amount of driving friction will be present between the line 3 and pulley 4. If the user releases the downward pull on the line 3, the line will no longer be tightly held against the pulley and the driving friction will be reduced to almost zero.

The contact between the line 3 and pulley 4 is thus controlled by the force that the user applies to the free end of the line.

Figure 7 shows a development of this construction, where the pulley 4 is carried on the shaft 26 which is seen to be supported by the walls of the tube 1. The shaft 26 has a drive coupling 27 at one side and this can be rotated by a motor 28. A support fork 29 attached to the impact tube 1 serves to support the motor and prevent any tendency for this to be rotated about the shaft 26.

The motor 28 is electrically operated and the necessary motive power for this action is delivered by a power cable 31.

In operation of the motor powered post driver apparatus, the user would put the motor into operation to drive the pulley 4 and then pull on the free end of the line 3. The line 3 would then be drawn into frictional contact with the vee shaped periphery of the pulley 4 and the line would be gripped causing the weight 2 to be lifted up in the impact tube 1. At the maximum necessary height of the weight 2, the user will interrupt the motor power supply and release the downward pressure on the line 3 free end. The line 3 will then become detached from its frictional contact with the vee pulley 4 and the weight will fall. The falling of the weight 2 will cause a blow to be struck on the post to be driven. Upon completion of the striking action, the user will restart the motor 28 and then pull lightly on the line free end. The frictional drive of the line 3 would then start again and the weight 2 will be drawn again by motor power up to the optimum lifting height.

The action can be repeated as often as necessary until the post has been driven in to the required depth. The amount of manual force required to be applied by the user is small because most of the work of lifting the weight will be done by the motor.

The operator has merely to apply small forces to the line free end to engage and disengage the frictional connection between the pulley and the line.

In yet a further embodiment, the switching of the motor could be effected semi-automatically by the movement of the weight in the tube so that the electrical circuit would be interrupted by the motion of the weight reaching the upper limit of its stroke.

The post driver apparatus of the invention has been found to be inexpensive to manufacture and since it is of lightweight construction it can be readily transported by hand to the site where it is required to be put into service.

The foregoing description of embodiments of the invention has been given by way of example only and a number of modifications may be made without departing from the scope of the invention as defined in the appended claims. For instance, instead of the wedges 13 being urged inwardly by the rubber rings 17, the rings could be replaced by springs. The spring 8 does not need to be the full length of the impact tube and it could be made shorter in length, if required. For example, the spring could be only one quarter of the tube length.