Known types of post drivers involves the use of a tall mast or guide on which a hammer is mounted. In use, the hammer is raised on the guide and is then allowed to fall under gravity to hit the post or a cap applied to the top of the post. The problem with such a device is that the mast needs to be very tall, for example four metres, making it difficult to work in confined spaces, for example under overhanging trees and one object of the invention is to provide an improved driver which will help to minimise that problem.

According to the invention there is provided a driver comprising a guide having a hammer thereon and operating means for urging the hammer along the guide to a position where it can apply a driving force, and means for reversing the operation of the operating means after the driving force has been applied so as to urge the hammer back along the guide.

By using operating means to urge the hammer into the position in which it can apply the driving force, the driver can be more compact than known types of post drivers making it much easier to use in confined spaces.

Preferably, the operating means is arranged to apply repeated back and forth movements to the hammer following an initial striking load applied by the hammer.

In a preferred embodiment, the operating means is connected to the hammer by means of a resilient device. In such a case, repeated back and forth driving movements of the hammer may be generated in response to the action of the resilient device following an initial striking load applied by the hammer. The resilient device may comprise a spring which compresses when the hammer is moved back along the guide. Additionally or alternatively, the resilient device may comprise a spring which compresses as a result of the operating means urging the hammer along the guide so as to apply the driving force. In a preferred embodiment, the resilient means comprises a pair of springs within a housing one of which springs may compress as the hammer is urged in a striking direction and the other of which springs may compress as the operating means urges the hammer in the opposite direction. The said springs may be coil springs preferably arranged substantially coaxially within the housing. Adjacent ends of the springs may be separated by a member through which the hammer can be moved by the operating means. The resilient means may comprise rubber springs.

The operating means for urging the hammer may comprise gas.

The operating means preferably includes an arm which may be arranged to move the hammer along the guide. The arm is preferably pivotally connected to a mounting.

The arm may also be pivotally connected to the hammer.

The aforesaid operating means may take the form of an actuator which is preferably fluid operable. The actuator preferably acts on the arm to move the arm about its pivotal connection to the mounting. Where the aforesaid actuator is provided, the actuator preferably acts on the arm at a point closer to the pivot which connects the arm to the mounting than to the point at which the arm is pivotally connected to the hammer. In that way, a short stroke of the actuator will provide a relatively large movement of the pivotal connection to the hammer. Therefore, the actuator can be fairly fast acting bearing in mind that a small stroke is all that is needed to move the hammer as required.

Preferably, the operating means is arranged to move the hammer in along the guide until a given parameter is sensed whereupon the operating means is arranged to reverse and move the hammer in an opposite direction. The parameter may, for example, comprise a fluid pressure or fluid movement sensor. The parameter is preferably sensed as the operating member continues to move the hammer back along the guide after the hammer has reached a limit of travel.

The operating means is preferably fluid operable and means may be provided in a fluid circuit for the operating means for reversing the operation of the operating means after the given parameter has been sensed. The means for reversing the operating means may be valve arranged to reverse fluid flow to the operating means on sensing the said parameter.

In a preferred embodiment, the guide is mounted on a carrier which enables the position of the guide to be adjusted. The adjustment feature is useful in that the carrier can be moved on a main support from a position in which it is effectively telescoped into the main support for compact stowage and transport, to an extended position. The adjustment of the carrier and hence the guide may be carried out by an actuator which may be fluid-operable.

Preferably, the guide is upstanding and the operating means arranged to move the hammer up and down on the guide. In such a case, and where the position of the guide can be adjusted, the guide may be adjusted in an up-and-down direction.

Holding means such as a removable pin may be provided for holding the carrier in its adjusted position. As the hammer is actually driven downwardly in such a case in order to apply a striking load, it is more effective than known types of drivers which rely on gravity alone The aforesaid mounting for arm is preferable on or part of the carrier.

An impact receiver such as a cap or cap-like member may be provided for location on the top of a member such as a post to be driven by the hammer and to which the striking load is applied by the hammer. In order to ensure that the impact receiver is held in contact with the member to be driven by the hammer during operation of the hammer, the actuator for adjusting the position of the carrier may be arranged to apply a load on the impact receiving member during operation of the hammer.

The operating means is preferably fluid operable and, in such a case, fluid in a circuit therefor may conveniently be used to operate the actuator for applying the load to the impact receiving member. The fluid from the circuit may pass through a pressure reducing means to operate the actuator for applying the downward load to the impact receiving member.

Mounting means may be provided for mounting the driver on a host vehicle such as a tractor. Alternatively, the host vehicle may be a front end loader or a host machine with an hydraulic arm for example a JCB or a three hundred and sixty degrees machine.

Preferably, the driver has ground engageable legs.

A driver in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which; Figure 1 is a perspective view of a preferred form of post driver in accordance with the invention; Figure 2 is a front view of the post driver of Figure 1 in the direction of arrow II in Figure 1; Figure 3 is a side view of the post driver in Figure 1 showing a hammer in position on a cap of the driver;

Figures 4 and 5 are views similar to Figure 3 showing the hammer in partly raised and fully raised positions respectively; Figure 6 is a rear view of the post driver shown in Figure 1 looking in the direction of arrow VI in Figure 1.

Figure 7 is a perspective diagrammatic view of a preferred form of post driver in accordance with the invention; and Figure 8 is a diagrammatic representation of part of a fluid circuit for the post driver of Figure 7.

Looking at Figures 1 and 2, the driver comprises a mast 10 (corresponding to the aforesaid carrier) formed from square cross section steel tube. On the front face of the mast 10, an upstanding guide 12 is mounted of I-shaped or T-shaped or other suitable cross section. One flange 14 of the guide 12 is secured to the post 10 and the other flange 16 forms a guide rail for a hammer 18. The rear face of the hammer 18 (see Figures 3 to 5) carries a runner arrangement 20 which slideably retains the hammer 18 on the flange 16.

The flange 16 also supports a cap 22 which has a slider arrangement 24 on its rear face. The slider arrangement 24 mounts the cap 22 slideably on the flange 16. A stop 26 is provided at the foot of the flange 16 to retain the cap 22 on the flange.

The cap 22 is generally rectangular and is shown in cross-section in Figures 2 to 5.

Cap 22 has metal side plates 28 which receive between them a rigid metal top plate 30. A dished metal plate 32 is mounted within the cap 22 immediately beneath the top plate 30. The cap 22 locates on the upper end of a post 34, the dished plate 32 serving to centralise the cap 22 on the post 34 as shown in Figures 3,4 and 5.

The rear of the mast 10 carries a mounting plate 36 formed with mounting apertures 38 which enable the mast to be carried by lifting arms 40 of a host vehicle such as a tractor. In another embodiment, the lifting arms 40 and the mounting plates 36 are not provided.

125 The upper end of the mast 10 forms a mounting 41 a front face of which is cut away to form an elongate aperture 42. Upper and lower stops 44,46 are mounted on the front of the mast 10 adjacent the upper and lower ends respectively of the aperture 42.

An arm 48 comprising two spaced apart plates 50 is connected at one of its ends to 130 the mounting 41 by pivots 52 and is pivotally connected at its other end to the upper end of a rod 54 of a resilient device 56. The lower end of the resilient device 56 is pivotally connected to the hammer 18 via brackets 58. As shown clearly in Figures 3 to 5, the arm 48 is pivotally connected close to the pivots 52 and between its ends to a push rod 60 of a hydraulic actuator 62. Preferably, the push rod 60 of the 135 actuator 62 extends between the two plates 50. A cylinder 64 of the actuator 62 is connected to sides of the mast 10 by pivots 66. The push rod 60 of the actuator 62 can be extended under hydraulic flow to raise the arm 48 or retracted to move the arm 48 downwardly. A hydraulic circuit for operating the ram 62 includes a reversing valve 68 and power for the hydraulic circuit is preferably derived from the 140 tractor which carries the post driver. The valve 68 may be of a type known as a Recip Valve available from BYPY, 8 Lingen Road, Ludlow Business Park, Ludlow, Shropshire SY8 1XD, England.

The resilient device 56 comprises a cylinder 70 having a closed lower end 72 and a closed upper end 74 which carries a collar 78 forming a sleeve bearing for the rod 145 54. The lower end of the rod 54 carries an annular plate 80 which is slideable along the cylinder 70. A lower spring 82 is held in light compression between the closed lower end 72 and the plate 80 and an upper compression spring 84 is held in light compression between the closed upper end 74 and the plate 80. The springs 82,84 hold the plate centrally within the cylinder 70. The springs 82,84 may be of a kind 150 of shock absorbing material typically used on a car suspension. If desired, gas, or rubber springs could be used instead.

In use, a post 34 is initially positioned where required and the tractor is manoeuvred so as to locate the cap 22 in position on the top of the post 34. The cap 22 is preferably positioned on the post 34 by means of a locating spike (not shown) which 155 depends from the cap. The weight of the post driver is primarily carried by the arms 40 and the arms 40 are lowered so as to position the cap as shown in Figures 3 to 5 with at least some of the weight of the post driver and the arms 40 being carried by the post 34. In that way, the cap 22 will remain in position on the post 34 during the hammer action of the post driver described below. The positioning of the cap 22 on 160 the post in that way will cause the mast to slide downwardly relative to the cap until a further stop indicated at 81 contacts the slider arrangement 24.

With the hammer 18 resting on the cap 22 in that way, hydraulic fluid under pressure is pumped into a port PI at the lower end of the cylinder 64 so as to extend the piston rod 60 and thereby retract the arm 48. A port P2 at the top of the cylinder 165 is connected to exhaust. Movement of the arm 48 is transmitted via the rod 54 to the springs 84 and hence to the cylinder 70. Once the compressive load applied to the spring 84 is greater than the downward load applied by the hammer 18 and the cylinder 70, continued retracting, i. e. raising of the arm 48 lifts the hammer 18 as shown in Figure 4. Lifting of the arm 48 continues until the arm 48 strikes the 170 upper stop 44. That causes a build up of hydraulic flow in the actuator 62 and when a predetermined pressure is reached the valve 68 which is pressure sensitive reverses the flow applied to the actuator 62 so that fluid under flow is now applied to the port P2 and PI is connected to exhaust. The applied pressure causes the piston rod 60 to be retracted very rapidly into the cylinder 64 thereby forcing the resilient 175 device 56 and hence the hammer 18 sharply downwards, the angular velocity of the left hand end of the arm 48 as viewed in the drawings being greater than that at the point where the arm 48 is connected to the push rod 60. An applied pressure of around 180-200 bar acting on an actuator piston of 63 mm diameter with a piston rod diameter of 38 mm will provide rapid downward propulsion of the hammer 18.

180 The hammer 18 is propelled downwards at a speed greater than would be achieved by free-fall alone until the hammer strikes the cap 22 thereby driving the post 34 into the ground, the arm 48 being spaced from the lower stop 46 at the point of strike. Continued pressure in the actuator 62 together with the downward force of spring 84 against the plate 80 urges the rod 54 into the cylinder 70 thereby 185 compressing the lower spring 82. The compression continues until a rapid build up of flow in the actuator 62 causes the valve 68 to reverse the flow of hydraulic fluid so that flow is once again applied to the port PI at the lower end of the cylinder 64.

The cycle then repeats itself. The fluid-operable control of the hammer 18 is useful in that the operation of the hammer can be stopped at any point in the cycle.

190 The post driver in accordance with the invention drives the post 34 very rapidly into the ground without the disadvantage of a tall mast. In fact, whereas prior art machines have masts within the region of 4m in height to facilitate sufficient free fall, a post driver in accordance with the present invention can use a mast as short as 2 metres. Also, whereas a free-fall system requires a hammer having a weight of 195 225 kg the weight of the hammer 18 in the present invention can be as low as 100 kg in view of the mechanically assisted downward force applied thereto by the actuator 62. In view of the reduced weight of the post driver compared to prior types, the driver can be mounted on, say, a telescopic handler of an agricultural vehicle enabling the vehicle to reach over obstacles such as ditches and hedges 200 which is not possible with prior art post drivers particularly in view of their height and weight.

Where the post driver is driven by the hydraulic system of a vehicle on which it is mounted, it is not necessary for an assistant to stand in the vicinity of the post driver as the user can sit of a vehicle itself thereby reducing the risk of danger to the user.

205 The post 34 may be a wooden or steel post.

Another advantage of using the system in accordance with the invention is that the reduced height of the mast 10 compared to the prior art enables more strikes per second to be achieved. Typically, known machines will provide a main hit every five seconds with one or two bounces following. With the embodiment of the present invention shown in Figures 1 to 7 a hit can be achieved at least every two seconds which is a considerable advantage.

Reference is now made to Figures 7 and 8. In those figures, parts which correspond to parts shown in Figures 1 to 6 carry the same reference numerals and will not be described in detail.

In Figure 7, the mast 10 is received slideably within a channel-shape cross section main support 90 which has in-turned edge sections 92 for retaining the mast 10.

The main support 90 carries two parallel hitch plates 94 at its rear end as viewed in the drawings, the hitch plates 94 being secured, say, by welding to opposite sides of the main support 90. The main support 90 is also pivotally connected to a ram 96 arranged between the plates 94. The plates 94 and the ram 96 can be used to secure the post driver to a tractor or suitable vehicle or machine. Extension or retraction of the ram 96 enables the mast 10 to tilt out of the vertical position if desired.

The lower end of the main support 90 also carries adjustable legs 98 and has its lower end closed by means of a plate 100. The plate 100 is attached to a cylinder 102 of a height adjustment actuator 104 which projects upwardly through the mast 10. The actuator 104 has a push rod 106 which is secured by an attachment (not shown) to the inside of the mast 10. Extension and retraction of the actuator 104 raises and lowers the mast 10, a slightly raised position of the mast 10 being shown in broken lines in Figure 7. The mast 10 carries two spaced-apart mounting plates 108 (constituting the aforesaid mounting). The mast 10 is formed with a further elongate aperture 42a opposite the aperture 42. The arm 48 extends through the aperture 42a and is pivotally mounted on a shaft 110 extending between the mounting plates 108. The lower ends of the plates 108 pivotally support the

cylinder 64 of the ram 62 and the push rod 60 passes between the spaced apart plates 50 of the arm 48 and is pivotally connected thereto by means of a pivot 112.

The mast 10 carries a downwardly projecting tube 114 which slidably receives a smaller tube, box section or bar 116 which, in the example shown, is fixed to one of the hitch plates 94. The tube 114 is formed with a plurality of apertures 118 which can align with one or more apertures 118,119 in the smaller tube 116. A pin 120 can be inserted through selected aligned apertures 118,119. Height adjustment of the mast 10 by means of the actuator 104 is carried out with the pin 120 withdrawn.

Once the correct height positioning of the mast 10 is achieved, a small further adjustment is made to align suitable apertures 118,119 and the pin 120 is inserted to lock the mast in the adjusted position. In Figure 7 the full line position of the mast is close to its lowest position. With the pin 120 in position, fluid pressure required to raise the mast 10 can be released.

Fluid to operate the actuators 62,104 is provided from a main supply 122 on a vehicle 124 to which the post driver is hitched. A fluid circuit indicated generally at 126 in Figure 8 includes a fluid flow reversing valve 128 for the actuator 62. The valve 128 acts in response to a fluid flow sensor 130. The actuator 104 receives fluid from the circuit 126 via a pressure reducing valve 134 of known kind whereby flow applied in chamber 132 is smaller than the pressure supplied to the actuator 62.

In use, the post driver is moved to a position where the cap 22 can be located on top of the post 34. Once the post driver has been manoeuvre to the desired position, the legs 98 are adjusted so as to contact the ground. In that way, the vehicle 124 does not need to support the weight of the post driver. Once the cap 22 is in position, the pin 120 is removed and fluid under reduced pressure is fed to the chamber 132 of the actuator 104 so that the actuator 104 draws the mast 10 downwardly. Such downward movement continues until the stop 81 (the stop 26 not being shown) contacts the slider arrangement 24 whereupon further downward movement of the mast 10 causes a load to be applied to the cap 22 and hence to the post 34. Where the ground is sufficiently soft, the load applied by the actuator 104 may be sufficient to begin or even complete driving of the post 34 into the ground.

Where it is necessary to use the hammer 18 fluid is fed to the actuator 62 and the 265 driver operates in the same manner as described with respect to Figures 1 to 6 except for the way in which the fluid is sensed to reverse fluid flow to the actuator 62.

In Figure 7 and 8, when the arm 48 is lifted until it strikes the upper stop 44, the flow sensor 130 senses a reduction in flow and the flow reversing valve 128 is 270 immediately operated so as to reverse the flow of fluid to the actuator 62. The arm 48 is then moved downwardly until the arm 48 makes contact with the lower stop 46 whereupon flow is reversed so that the actuator 62 lifts the arm 48 again. It has been found that the use of a flow reversing valve 128 leads to a much faster operation of the post driver. Moreover with the arm 48 being longer than the arm 48 275 in Figures 1 to 6, a greater operating speed of the hammer 18 is achieved under the action of the actuator 62 for a relatively small stroke of approximately 2.5 inches (approximately 6 cm). With the embodiment of Figures 7 and 8 it has been possible to achieve around 70 hits on the cap 22 per minute.

As the post 34 penetrates the ground, the constant pressure in the chamber 132 of 280 the actuator 104 ensures that the cap 22 follows the post 34 and remains in contact therewith.

If desired, the cap 22 could be replaced by a chisel or spike to enable the driver to be used to break up a hard material such as concrete.

If desired the mast 10 could be connected to the post 34 by means of a chain or 285 shackle to enable the post 34 to be extracted from the ground. In such a case, the actuator 104 moves the mast upwardly to exert an upward extraction force on the post 34. Typically, a pressure of around 2500 psi could be used when extracting a post 34 in that way.

The pressure applied to the chamber 132 to provide the constant downward load on the mast 10 may be around 500 psi whereas the pressure applied to the actuator 62 will be much higher, for example, around 2500 psi.

Instead of hammering a post 34 into the ground, the driver may drive a cylindrical shell into the ground into which the post 34 can subsequently be inserted.

In another embodiment of the invention (not shown) the main support 90 does not carry hitch plates 94 and a ram 96. Instead, the smaller tube, box section or bar 116 is of greater length and it extends to locate adjacent the plate 100 of the main support 90. In that case, the bar 116 sits on a separate flat plate (not shown) which is attached to the host machine.