A conventional rock breaking machine is illustrated in Figure 1 of the accompanying drawings. This type of equipment is conventionally known as a"stationery"or"pedestal"rock breaker and typically comprises the arm of an excavation bucket from which the bucket itself has been removed and replaced with a percussion head comprising an air or hydraulically powered reciprocating piston which hits a steel moil or tool mounted thereto for breaking rocks located in the vicinity of the rock breaker. Such machines can be located, for example, adjacent the mouths of furnaces to break slag or to clean the mouths of ladles. Where necessary, these devices can also be mounted on tractors or other appropriate mobile means, so that the device can be moved fairly easily from one location to another as might be required. Various positions of the extension ann are shown in Figure 1.

Conventional rock breaking machines utilise a great deal of relatively sophisticated tool manoeuvring equipment which is expensive and which itself requires a great deal of room in which to move. A conventional machine of the type illustrated in Figure 1 is by its very nature extremely large and often requires a concrete foundation in order to be supported properly while the rock breaking head is being manoeuvred in confined areas over"grizzley"bars or within the bowels of crushers, for example, to break or remove rocks and rubble which become jammed.

In order effectively to cover the working area defined by the grizzley bars, a long reach for such a conventional crushing device is essential and this adds to its size and cost. More often than not, the breaking of a jammed rock caught between the bars of a"grizzley"is not required and the rock can be freed simply by rolling it over so that its minimum dimension can pass between the gap. The construction of such a device does not allow it to move or roll rocks in a circumferential direction with respect to its base.

Although such a device can move rocks with relative ease in a radial direction, it is extremely difficult to control the rock breaking tip with any accuracy of movement when attempting to dislodge a rock in a circumferential direction particularly when the rock is remotely disposed away from the base of the device.

It is with these problems in mind that the inventor has directed his thoughts to the present invention.

SUMMARY OF THE INVENTION According to the invention there is provided a pendent rock breaking device comprising : a boom having means for mounting a rock breaking tool thereto ; support means for hanging the boom directly from an overhead fixture over a rock breaking area ; and pivot means provided at or towards one end of the boom allowing the boom to be pivoted freely in use in any direction over the rock breaking area.

The boom may comprise at least one retractably extendable hydraulic cylinder operable to urge a rock breaking tool fitted to the device towards or away from the rock breaking area.

Preferably, the boom has power means for causing the tool to vibrate, alternatively compactor means for dislodging, vibrating and/or compacting material located in use beneath the boom.

The rock breaking device may comprise means for adjusting the angle of inclination of the boom in use so that a rock breaking tool fitted thereto can be directed towards different regions within the rock breaking area. The angle adjustment means preferably fix the boom at a chosen angle in use.

The boom angle adjustment means may comprise a pair of telescopic hydraulic cylinders arranged to act between the boom and the overhead support, or the overhead or an adjacent fixture. Preferably, the adjustment cylinders act on the boom in planes disposed substantially orthogonally to each other.

The invention also provides a method of breaking rocks comprising the steps of :- hanging a boom from an overhead fixture over a rock breaking area ; mounting a rock breaking tool to the boom, and adjusting the angle of inclination of the boom in use to direct the tool to different regions within the rock breaking area.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example only with reference to the accompanying drawings, in which : Figure 1 shows a conventional rock breaking device; Figure 2 shows a schematic front view of a rock breaking device according to the invention (two lateral positions of the rock breaker either side of the central position are also shown in schematic form) ; Figure 3 shows a schematic side view of the device shown in Figure 2; Figure 4 shows a schematic top view of the device shows in Figures 2 and 3; Figure 5 shows a pictorial view of a preferred embodiment of a rock breaking device according to the invention ; and Figure 6 shows a pictorial view of an alternative embodiment of a rock breaking device according to the invention.

DESCRIPTION OF EMBODIMENTS Figure 1 shows a conventional rock breaking machine of the type discussed above.

A pendent rock breaking device 10 according to the invention is illustrated in Figures 2 to 5 of the accompanying drawings. The device has a boom 12 which carries means at its operatively lower end for mounting a rock breaking tool or moil 14. Near this end, a power means, in the form of a percussion head 16, is located. The head 16 comprises a reciprocating piston (not shown) which impacts on the tool 14 causing it to vibrate in use to break rocks into smaller pieces.

At the operatively upper end of the boom 12, a support means in the fonn of a plate 18 is provided for hanging the boom 12 from an overhead support It is not necessary for the suspension means to be provided in the form of a plate, although this may be preferable for strength in certain circumstances.

In appropriate situations, the boom 12 could be mounted directly to a man- made or natural fixture such as a hanging wall over an ore pass or chute, for example, underground in a mine. Nevertheless, even in this simplified version, it is envisaged that the boom will have some or other formation on it, herein termed support means, for suspending the boom in use from a fixed position on an overhead support.

What is of importance to the invention is that at or towards the operatively upper end of the boom, a pivot means 20 is provided which allows the boom to be pivoted freely in use in more than one plane while hanging over the rock breaking area, shown generally by the numeral 24 in Figure 2 of the accompanying drawings. A"grizzley"bar is visible at 25. In this version of the invention, the pivot means 20 is provided in the form of a universal type joint which can be seen in more detail pictorially in Figure 5 of the accompanying drawings. This construction of pivot means allows the boom to pivot in any direction while hanging from the pivot means 20. In Figure 5 of the accompanying drawings, a robust support means is shown in the form of a thick steel plate 18. To this plate, the universal type joint 20 is welded at 22. As an alternative construction, the upper section 26 of the universal joint 20 could be fastened (by means of a rock anchor or bolt) directly to an overhanging rock face and in this way the universal type joint 20 would comprise both the support means and pivot means required to put the invention into practice in its preferred form.

The boom 12 comprises, as shown, a retractably extendable hydraulic cylinder which is operable, by means of feed and exit pipes numbered 28 and 30 in Figure 5, to urge the rock breaking tool 14 towards or away from the rock breaking area 24. In this way, the tool 14 can be brought against a rock to be crushed and then vibrated (or"fired"as is referred to in the art) as appropriate by the percussion head 16 to crush or fracture the rock.

The device 10 comprises two further telescopic hydraulic cylinders 32 and 34 which are arranged to act between the boom 12 and the overhead support plate 18, in the manner illustrated in Figure 5 of the accompanying drawings. The cylinders 32 and 34 are used to adjust the angle of inclination of the boom 12 in use. Once again, the overhead support could be in the form of a hanging wall in a confined location underground and the upper ends of the boom adjustment cylinders 32 and 34 could be mounted to the overhead support in this natural form at discrete locations adjacent to the central support means 18. At each end of the adjustment cylinders a Sexural joint 35 is provided. A universal type joint as shown at 20 could be used with equal facility.

Conveniently, it has been found to arrange the cylinders so that they act on the boom 12 in planes which are disposed substantially orthogonally to each other. This arrangement can best be seen in Figure 4 of the accompanying drawings, where the substantially orthogonal angle between the adjustment cylinders 32 and 34 is marked with the arrow A. Of course, as the cylinder 32 and 34 extend and retract in use, their respective planes of action will not always remain exactly at right angles to each other.

In alternative configurations of the adjustment cylinders, four such cylinders could be arranged equally around the central boom to act between upper and lower reaction arms extending radially away from the boom itself. In this configuration, each pair of opposing cylinders would act in the manner of a movable parallelogram as it were, with one cylinder extending while the other contracts. Further, such an arrangement with appropriate hydraulic control would allow the adjustment cylinders to assist in, or develop themselves, the longitudinal thrust downwards when extension of the boom is required. In a more simple arrangement, two cylinders could be mounted between extension arms at either end of the boom to act in planes substantially at right angles to each other.

When mounted in any one of the configurations discussed above, the cylinders 32 and 34 can impart components of radial and circumferential directions of movement to the rock breaking tool 14 with respect to the central support means 18. This provides an important characteristic to the invention in that rocks required to be broken within the rock breaking area can be nudged or rolled radially inwardly to be disposed more directly underneath the boom 12. It has been found that rocks can be broken effectively with the boom 12 inclined at an angle to the vertical of approximately 20° (angle B in Figure 2). In the range of inclinations of 20° to 45°, rocks can be"pulled in"as it were to the rock breaking 20° zone.

For angles of inclination which are greater than 45°, the rocks tend to be pushed away.

For the target rock breaking zone to be increased effectively, it is required only to increase the height of the support means 18 above the rock working area 24 by a small distance. The effective rock breaking area increases in proportion to the square of the increase in height of the support means 18 above the rock breaking area 24. A circular effective rock breaking area (27 in Figure 4) is defined by the rock breaking device 10 illustrated in the accompanying drawings. The average height of the pivot means 20 above a set of grizzley bars will typically in use be approximately 3,5 to 4 meters.

At this height, a grizzle bar array of conventional size (29 in Figure 4) will fall within the effective target area of the rock breaking device. If necessary, the hanging wall above the grizzley bars can be hollowed out to accommodate the pivot means 20 further away from the working area. A conventional machine in such a situation would have to reach in from the side and would need a massive support structure to accommodate the forces imposed by the cantilever nature of the extension arm. Such arrangements require large amounts of space and do not work effectively.

As illustrated in Figure 5, the adjustment cylinders 32 and 34 are powered by feed and exit hoses 36 and 38, and 40 and 42 respectively. Control means (not shown) are provided to operate the device in use. Typically, a remote pilot control, for example a manual joystick, will be utilised to control the respective extensions and retractions of the angle adjustment cylinders 32 and 34. A separate manually operated lever will be provided to control the longitudinal extension of the boom 12 and, for convenience, a push button will be provided to the end of this lever for"firing"the tool 14.

Reference is now made to Figure 6 of the accompanying drawings which depicts an alternative embodiment of a rock breaking device according to the invention. This embodiment is very similar to the embodiments previously described and like components are referred to with the same numerals as above. Accordingly, the rock breaking device 10 comprises a boom 12, a rock breaking tool 14, a power head 16 and angle adjustment cylinders 32 and 34. (Only cylinder 34 is visible in the view given in the accompanying drawing Figure 6).

The boom 12 is attached to a pivot point 20 to an overhead fixture and a universal type joint (of similar construction) is provided at the upper end of the angle adjustment extension cylinders 32 and 34 at the position 35.

The important distinction to note on the embodiment depicted in Figure 6 is that the extendable boom 12 has a central feed guide tube 46 which is of square section. This prevents rotational movement of the power head 16 about the longitudinal axis of the boom. This, in turn, allows the guide rods 48 depicted in Figure 5 of the accompanying drawings to be dispensed with.

Longitudinal extension and retraction of the boom 12 is provided by extension cylinders 50 and 52 positioned on either side of upper fixed portion 54 of the boom 12. The extension cylinders 50 and 52 are connected to one source and work together in tandem. They act simply to extend or retract the boom 12 in use to urge the tool 14 towards or away from the material to be worked in use. The extension cylinders 50 and 52 are disposed equally away from the longitudinal axis of the boom 12 and therefore impart a balanced extension force on the tool 14 in use. This reduces excessive wear on the reaction pads built into the device (not shown).

It will be appreciated that for any of the embodiments of the invention thus far described, the"angle adjustment"arms 32 and 34 need not be fastened at their upper ends to the same fixture to which the boom 12 is attached at the pivot point 20. The"angle adjustment"arms 32 and 34 need only be fastened to a fixture adjacent the boom 12 to thereby impart a lateral force from the boom 12 to allow it to move in use in the manner described above.

These arms, moreover, need not act in planes which are mutually orthogonal, as long as they act in directions which impart components of radial movement to the boom 12 about its pivot point 20. It is believed, nevertheless, that a disposition of 90"between the respective planes in which the extension arms 32 and 34 act provides for a greater degree of flexibility.

A drive unit 56 is shown adjacent the rock breaking device 12 and an operations console is also illustrated at 58 at which an operator 60 is seated.

"Proportional"joystick control is provided for the device 10 and allows more than one"function"of the boom to be carried out simultaneously. In other words, an extension of the boom can be caused at the same time as an angle adjustment whilst powering the powerhead 16. Typically, one joystick will be allocated to the control of the boom's radial position in use, while the other joystick will be used to control the extension of the boom and the operation of the powerhead 16 by means of a"fire"button. Proportional joystick control ensures that the angle of the boom (in any particular orientation) is"proportional"to the angle of the joystick controlled by the operator 60.

For any of the embodiments of the invention thus far described, an optional "multi-stage"feature can be incorporated into the device 10. In order to provide a more compact device (particularly in circumstances where there is not much operational head room between the hanging wall and the grizzley to be worked) the boom 12 can be provided in"multi-stage"form. In other words, the extensible cylinder comprising the boom 12 can be provided in a number of telescoping units, typically three, which can be caused to extend in sequential fashion to allow a greater degree of extension for a proportionally smaller sized rock breaking device 10. In a more sophisticated version of the invention, the boom 12 can be extended so much that the impactor 14 can be caused to impact on rocks situated well below the bars of the grizzle through which the run of mine material is to be passed. In this way, a boom 12 comprising an overall retracted length of typically 2,75 meters can be extended to an overall reach of 11 meters. In all other respects, the"multi-stage"rock breaking device 10 works in exactly the same way as previously described.

If necessary, a rock breaking device 10 according to the invention can be mounted in the orientation shown on overhead rails to traverse a working area of larger size, for example to clear chute areas positioned beneath discharging locomotive trucks.

The boom 12 of the device 10 according to the invention can be installed relatively easily. The overhead hanging wall is first cleared up to define a reasonably flat surface. A large flat surface area is not necessarily required in view of the almost point contact between the boom to the overhead support A suspension eye or other appropriate element can then be fastened to the hanging wall by means of long roof bolts, for example. If necessary, an epoxy adhesive can be used to reinforce the attachment point A temporary support plate is then positioned over the grizzley bars and the boom lifted into a substantially vertical orientation thereon. By using temporary power to the boom, it can be extended so that the pivot means 20 at its upper end can be fastened to the suspension eye already installed. This method of installation does not require the use of overhead cranes or extensive rigging equipment. Similar methods can be used to install the adjustment cylinders.

The rock breaking device according to the invention can be used with great effect in confined areas where falls of ground are frequent requiring the use of a rock breaking device on a substantially full time basis to clear rocks jammed in an ore pass entry.