BACKGROUND OF THE INVENTION:

1 . Field of the Invention:

[0001 ] This invention relates to a sharpening system.

[0002] The invention particularly relates, but is not limited to, a sharpening system for the knives or blades of chipper drums e.g. of the type fitted to tree harvesters suitable for harvesting shrubs, coppice, or tall single stem trees, where such trees are planted at preferably regular spacing in rows.

[0003] The invention also provides a sharpening system for sharpening the knives or blades of stationary chipping machines; and for sharpening the knives of disc chippers.

2. Dictionary

[0004] The terms "knife" and "knives" will be used throughout the specification to also include a "blade", or "blades" for a chipper drum.

[0005] The term "trees" shall be used throughout the specification to describe shrubs and trees which have either a single-stemmed form; or a plurality of coppice stems extending generally upwards from a tree stump or lignotuber; and by example, includes trees of the Eucalyptus and Acacia genera indigenous to Australia; and of the Salix and Populus genera indigenous to Europe and North America.

[0006] The term "harvester" will be used throughout the specification to define a chipper device, mounted to a mobile vehicle that moves along row of trees, continuously chipping each stem into a desired particle size; or to a fixed machine to which the trees are delivered are being cut down.

[0007] The term "pour rate" will be used throughout the specification to define the speed that chipped material flows through the chipper drums and is measured in green metric tons per hour. This is an important measurement of performance of the chipper drums (and thereby, the tree harvesters.) 3. Prior Art

[0008] NB: The following discussion is by way of background information only, and is not to be considered a statement of the common general knowledge (CGK) in the area of technology, anywhere in the world.

{0009] It has been proposed, internationally, to grow trees (as hereinbefore defined) of the Eucalyptus, Populus and Salix genera as an ecologically- based energy and fiber feedstock.

[0010] As the Eucalyptus, Populus and Salix genera are fast-growing, their biomass can be used as a "renewable" source of energy, fibreboard or paper pulp, as the trees can be harvested every 2-6 years.

[001 1 ] The key challenge has been the ability to economically chip the trees and transport the chipped biomass from the tree growing areas to industry processors e.g., fiberboard and paper manufacturers, electricity generators, heat users and biofuel convertors.

[0012] Efforts to solve this challenge have initiated research to develop efficient continuous tree chipper harvesters in Australia to improve pour rate productivity measured in terms of weight or volume per hour, thereby reducing the cost of chipping trees.

[0013] Examples of two such "PRIOR ART" prototype continuous tree chipper harvesters will now be described.

[0014] International Patent Application PCT/AUOO/00171 (= International Publication WO 00/52998) (Oil Mallee Company of Australia Pty Ltd) discloses a tree harvester ("the Giles harvester") mounted on a tractor, where transport means, in the form of vertically-spaced endless chain conveyors, engage the substantially vertical tree stems just before the trees are cut adjacent the bases of the stems by a rotary saw. The transport means convey the tree stems, in a substantially vertical position, towards a chipper drum rotating about a substantially horizontal axis. Counter-rotating feed rollers, and an adjustable anvil, mounted adjacent to the chipper drum, direct the stems of the trees into the chipper drum at an angle between 90° and 30° from the vertical, with the stems being guided and supported by a pair of adjustable plates while being chipped. By adjusting the location of the plates and the anvil relative to the (conventional) chipper drum, a wide range of trees can be harvested.

[0015] International Patent Application PCT/AU2010/000403 (= International Publication WO 2010/129986) (Future Farm Industries CRC Limited) discloses a tree harvester ("the Sulman harvester") which has advantages over the Giles harvester, in that the tree stems are fed substantially vertically to a chipper drum, rotating about an axis inclined at a small angle to the horizontal axis, and parallel with the direction of travel of the tree harvester. At least one pair of opposed nip rollers feed the tree stems downwardly, and rearwardly, to the chipper drum, so that the tree stems are progressively chipped as they are fed into, and along, the full length of the chipper drum. Unlike the Giles harvester, no energy and time is wasted in tipping the tree stems from the original orientation in which they are feed to the chipper drum, and the wear on the knives of the chipper drum is more evenly spread along the length of the chipper knives, extending the periods between re- sharpening. In addition, the parallel orientation of the chipper drum enables the simultaneous chipping of two or more stems in single file. This results in greater operational and energy efficiency, leading to a higher pour rate for the Sulman harvester than is possible by the Giles harvester.

[0016] Both the Giles and Sulman harvesters have advantages over previous tree harvesters for smaller trees, where many of those harvesters were based on forage harvesters, originally designed for harvesting thin stemmed cereal and grass crops, and horizontal disc chippers for discrete vertical chipping of individual tree stems.

[0017] The efficiency of chipping depends on many factors, including chipper knife wear. A sharp knife is a prerequisite for chips of good quality and reduced chipping energy. Worn knives give an uneven chip surface, which gives rise to higher amounts of pin chips and fines, and increases plastic deformation of the chip ends. [0018] Research demonstrates that knife wear will result in a sharp drop in productivity (>20%) and adversely affects chip quality. Increasing the frequency of wet-sharpening sessions drastically enhances machine performance and reduces biomass processing cost. Since benefits largely exceed costs, increasing the frequency of wet-sharpening sessions is an effective measure for reducing overall chipping cost. However, based on the construction of wood chippers, chipper knife removal is a regular and slow process that involves Occupational Health & Safety (OHS) concerns for those changing sharp steel knives. Also, the time spent replacing chipper knives can be as high as one hour per shift, directly reducing productive machine hours.

[0019] If the main goal of a chipper operator is to increase productivity and decrease fuel consumption, then managing knife wear in-situ, by fitting an automated wet grinding device, is a necessary step.

[0020] Currently, auto sharpeners are fitted to forage harvesters that chop various small to medium sized stems. In principle, the chopper drum spins, while a static grinding stone is traversed across the drum face, incrementally fed in with each pass. This sharpening device results in one key geometry flaw that increases specific energy consumption. Based on the radial grinding method, there is no clearance angle (a) provided, therefore material (e.g. tree stems) being fed in will rub the outer radius of the chopper drum causing friction and significant energy losses. The clearance angle is also called the 'pull in angle'. Rural Industries Research and Development Corporation (RIRDC) trials in 2003 demonstrated a 50% increase in specific energy consumption when the clearance angle (a) was absent from the knife geometry.

[0021 ] Wear of the knives on disc chippers also results in increased fuel consumption, reduced productivity and poorer quality chips for the same reasons as hereinbefore described.

OBJECTS OF THE INVENTION: [0022] It is an object of the present invention to provide an in-situ sharpening system for the knives or blades of chipper drums (e.g. for tree harvesters), or disc chippers, which overcomes, or at least ameliorates, one or more of the problems with existing knife sharpening apparatus and methods.

[0023] Other preferred objects of the present invention will become apparent from the following description.

SUMMARY OF THE INVENTION:

[0024] In one aspect, the present invention resides in an in-situ sharpening system for the knives of a chipping drum or a disc chipper, the chipping drum or disc chipper being rotatable about an axis of rotation, the system including:

a support adjacent the chipping drum or disc chipper;

a sharpening head, having at least one rotatable sharpening stone;

a first carrier, on the support, operable to move the sharpening head in a direction substantially parallel, or transverse, to the axis of rotation;

a second carrier, movably mounted on the first carrier, supporting the sharpening head and operable to enable the sharpening head to move in a direction substantially transverse, or parallel, to the axis of rotation; and first drive means to rotatably drive the sharpening stone when the sharpening stone is in engagement with, and moved along, a cutting edge of one of the knives.

[0025] Preferably, the sharpening stone is rotatable about an axis of rotation substantially transverse to the axis of rotation of the chipping drum, or substantially parallel to the axis of rotation of the disc chipper..

[0026] Preferably, the first carrier includes a track mechanism which guides the movement of the second carrier.

[0027] Preferably, the first carrier includes at least one reversible motor, operably connected to a continuous chain, cable or belt within the guide track; and the second carrier is operably connected to the continuous chain, cable or belt to enable the reversible motor to selectively move the sharpening head along the second carrier in a reciprocating motion.

[0028] Preferably, the second carrier has a carrier base plate movable along the guide track; the sharpening head is slidably mounted on the carrier base plate; and a stepping motor on the carrier base plate is operably connected to the sharpening head to move the sharpening stone towards, or away from, one of the knives to be sharpened..

[0029] Preferably, alignment means are provided between the support and the chipping drum or disc chipper to align the sharpening head to the adjacent one of the knives before the sharpening stone engages the cutting edge of the adjacent one of the knives.

[0030] In a second aspect, the present invention resides in a method of in- situ sharpening a knife of a chipping drum or of a disc chipper, the chipping drum or disc chipper being rotatable about an axis of rotation, the method including the steps of:

a) providing a support adjacent the chipping drum or disc chipper; b) providing a sharpening head with at least one rotatable sharpening stone;

c) providing a first carrier, on the support, operable to move the sharpening head in a direction substantially parallel, or transverse, to the axis of rotation;

d) providing a second carrier, movably mounted on the first carrier, supporting the sharpening head and operable to enable the sharpening head to move in a direction substantially transverse, or parallel, to the axis of rotation; and

e) providing a first drive means to rotatably drive the sharpening stone;

f) engaging the sharpening stone, when rotating, with a cutting edge of one of the knives; and

g) moving the sharpening head relative to the knife while the sharpening stone sharpens the cutting edge. [0031 ] Preferably, the sharpening head is moved along the knife with a reciprocating motion.

[0032] Preferably, the second carrier advances the sharpening head, selectively or incrementally, towards the knife as the cutting edge is being sharpened.

[0033] Preferably, before step f), an alignment means brings the sharpening stone into alignment with the cutting edge to be sharpened.

[0034] Other features of the present invention will become apparent from the following description..

BRIEF DESCRIPTION OF THE DRAWINGS:

[0035] To enable the invention to be fully understood, and to enable the skilled addressee to put the invention into practice, a number of preferred embodiments will now be described, with reference to the accompanying illustrations, in which:

FIG. 1 is a schematic view of a portion of a tree harvester provided with a chipper drum and a first embodiment of the sharpening system in accordance with the present invention;

FIG. 2 is a schematic control circuit measuring engine performance to initiate the sharpening system;

FIG. 3 is an isometric view of the chipper drum provided with the sharpening system, parts being omitted for clarity;

FIG. 4 is an end view corresponding to FIG. 3;

FIG. 5 is a similar view to FIG. 3, from the opposite side, where the anvil assembly has been omitted for clarity;

FIG. 6 is an isometric underside view of the sharpening head;

FIG 7 is an isometric view of the anvil assembly for the chipping drum, provided with an auto-adjustment system;

FIG. 8 is a similar view, on enlarged scale, of one portion of the anvil of FIG. 7; FIGS. 9 and 10 are respective schematic end views showing the arc of travel of the knives of the chipping drum relative to the anvil;

FIG. 1 1 is a schematic control circuit diagram for the auto-adjustment system for the anvil assembly;

FIG. 12 is a schematic control circuit diagram for the sharpening system;

FIG. 13 is an isometric view of a second embodiment of the sharpening system for sharpening the knives of a disc chipper; and;

FIG. 14 is a schematic circuit diagram of the controls for the sharpening system of FIG. 13.

[0036] NB: Any annotations on the drawings are by way of illustration only, and are not limiting to, or form part of, the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

[0037] Referring to FIG.1 , the sharpening system 10 of a first embodiment of the present invention is provided adjacent a chipping drum 40 and associated anvil assembly 60 of a tree harvester H, parts of which are omitted for clarity. Trees T are harvested in rows and the upper portions are defoliated by a flailer F. The trees T are fed substantially vertically through a pair of nip rollers NR to the chipping drum 40. The chips travel up through an outlet passage OP to a bin or hopper (not shown), which may be towed by the harvester H or hauled alongside the harvester H. A mass flow sensor MFS monitors the pour rate of the chips through the chipping drum 40 and out the outlet passage OP.

[0038] Referring now to FIG. 2, a CPU can monitor the pour rate via the mass flow sensor MFS and the fuel consumption of the engine E. When fuel consumption for the engine E exceeds a first preset limit for the pour rate of the chips, a warning signal sent be sent to the operator's station OS warning the operator that the chipping drum knives will shortly need sharpening and e.g. can be carried out at the next break in operation e.g. for refueling the harvester H or during the operator's scheduled break. Id a second preset limit is reached, the CPU can send a signal to the operator's station OS that the harvester must be stopped to enable the knives to be sharpened immediately, as the fuel consumption is such that the operation of the harvester H is now, or becoming, uneconomic.

[0039] The skilled addressee will appreciate that the CPU can be "mapped" so that different types of trees being harvested can be allowed for - typically the fuel consumption rate for softwoods will be lower than for harder woods. In addition, the CPU can taken into consideration the ground speed of the harvester H along the rows of trees T and/or other factors which may affect the fuel consumption rate.

[0040] Referring to FIGS. 3 to 5, the chipping drum 40 has a shaft 41 which rotates about an axis of rotation 42, driven a hydraulic motor (not shown) operably coupled to the shaft 41 . The shaft 41 is journalled in bearings 43 and is selectively rotatable by an alignment mechanism 80, having a stepping motor 81 connected via a belt 82 to a pulley 83 on the shaft 41 .

[0041 ] The alignment mechanism 80 further includes a ram 84 with a reciprocating finger or rod 85, the distal end of which is engageable in complementary locating holes 86 in the adjacent end plate 44 of the chipping drum 40.

[0042] The chipping drum 40 has respective end plates 44, 45 interconnected by a substantially cylindrical drum body 46, which is configured with, in this example, four elongate knife mounting assemblies 47 adjacent elongate recesses 48 in the drum body 46. Each knife mounting assembly 47 has a shoe 49 to which respective knives 50 are releasably secured by bolts 51 .

[0043] Each knife 50 has an elongate knife body 52 secured to a respective shoe 49, and has a cutting edge 53 extending forwardly of the shoe 49 (and overlying a respective recess 48 in the drum body 46. The cutting path 54 described by the tips of the cutting edges 53 is indicated in dashed lines in FIG. 4. [0044] Referring to FIGS. 3, 4 and 7, the anvil assembly 60 has an anvil head 61 supporting a plurality of anvil plates 62, releasably mounted on the anvil head 61 by studs 63. A pair of mounting plates 64 are mounted on the harvester, and each mounting plate 64 has an elongate slot or guide hole 65 which slidably receives a respective guide pin 66 adjacent the upper ends of the end plates 67 of the anvil head 61 .

[0045] An anvil control ram 68 has its cylinder 69 mounted on the harvester and the distal end of the piston rod 70 is connected to the distal end of a control lever 71 , the proximal end of which is secured to one end of a shaft 72 fixed in, and interconnecting, the lower portions of the end plates 67 of the anvil head 61 .

[0046] By extending or retracting the piston rod 70, as illustrated by arrow A in FIGS. 3 and 4, rotation of the shaft 72, as illustrated by arrow B, causes the anvil head 61 to rotate (and also move up or down relative to the mounting plates 64 by sliding movement of the guide pins 66 in their respective guide holes 65). This movement of the anvil head 61 moves the anvil plates 62 towards, or away from, the knives 50 of the chipping drum 40, as illustrated by arrow C. The anvil head 61 is selectively moved towards, or away from, the path 5 of the knives 50 to achieve the best chipping outcome for the trees T being harvested.

[0047] The sharpening system 10 will now be described in more detail with reference to FIGS. 3 to 6.

[0048] The sharpening system 10 is mounted on the harvester H, adjacent the chipping drum 40, as illustrated in FIGS. 1 and 2.

[0049] The first carrier 1 1 , mounted on the harvester H, has a pair of spaced guide rails 12, 13, interconnecting the end housings 14, 15, to form a guide track 16 which lies substantially parallel to, but spaced from the axis of rotation 42 of the chipping drum 40.

[0050] The first carrier 1 1 has a reversible motor 17 with a shaft 18 to operably drive a continuous chain or cable (not shown) , within the guide track 16, and passing around respective sprockets or sheaves within the end housings 14, 15 at the respective ends of the first carrier 1 1 . The chain or cable is operable to selectively move the second carrier 20 along the guide track 16 in the direction of arrow X.

[0051 ] The second carrier 20, illustrated in larger scale in FIG. 6, has a carrier base plate 21 , to which are secured guides 22 which slidably engage the guide track 1 6 of the first carrier 1 1 . A stepping motor 23 is mounted on the carrier base plate 21 , via a mounting bracket 24, and is operable to drive a travelling nut (not shown) within a sharpening head 25 to move the sharpening head 25 relative to the carrier base plate 21 in the direction of arrow Y.

[0052} A sharpening stone 26 is mounted on the distal end of the drive shaft 27 of a drive motor 28, mounted on the sharpening head via a bracket 29.

[0052] A grinding fluid is dispensed from the sharpening head 25, to the cutting edge 53 of an adjacent knife 50, from a hose 30 connected to a supply (not shown) of the grinding fluid. (Compressed air may be directed onto the cutting edge 53, after the sharpening stone 26 has passed, to assist in removing any residue from the sharpening operation. Such residue may be flushed away by the grinding fluid, which may also operate to cool the just-sharpened portion of the cutting edge 53.

[0053] A sensor 31 , with probe 32, is mounted on the sharpening head 25 to isolate the first- and -second carriers 1 1 , 20 and/or the sharpening head 25, if the sharpening head 25 is advanced too close to the chipping drum 40 or knives 50; or if the sharpening stone 26 has moved past the cutting edge 53 of the adjacent knife 50.

[0054] As will be appreciated by the skilled addressee, when the sharpening system 10 is brought into operation, the reversible motor 17 of the first carrier 1 1 will be operated to move the second carrier 20 to one end of the guide track 16, and thereby to one end of the cutting edge 53 of an aligned knife 50. Usually, the drive motor 228 on the sharpening head 25 will commence driving the sharpening stone 26 before the latter engages the cutting edge 53. The stepping motor 23 of the second carrier 20 is then operated to advance the sharpening head 25, and thereby the sharpening stone 26, towards the cutting edge 53. When the sharpening stone 26 engages the cutting edge 53, and grinding fluid is applied to the cutting edge 53 via hose 30, the reversible motor 17 of the first carrier 1 1 will be operated to move the second carrier 20, and the sharpening head 25, along the guide track 16, on the second carrier 1 1 , towards the other end of the cutting edge 53. At the end of the first sharpening pass along the cutting edge 53, the stepping motor 23 of the second carrier 20 will advance the sharpening head 25 one increment of distance; and the sharpening head 25 will travel along the guide track 1 6 in the opposite direction on the second sharpening pass.

[0055] With each change of direction of the sharpening head 25, the second carrier 20 will advance the sharpening head 25, until the cutting edge 53 is sharpened to the desired sharpness / cutting profile.

[0056] When one knife 50 has been sharpened, the sharpening head 25 is retracted by the second carrier 20; the next knife 50 on the chipping drum 40 is brought into alignment, and the chipping drum 40 is locked agai nst rotation by the alignment mechanism 80; and the sharpening sequence is repeated. The sequence of releasing the chipping drum 40; rotating a knife 50 into alignment; locking the chipping drum 40; operating the sharpening system 10 to sharpen the cutting edge 53 on the knife 50; and retracting the sharpening system 10; is repeated until all the knives 50 have been sharpened.

[0057] As hereinbefore described with reference to FIG. 2, the sharpening system 10 can be operated when the fuel consumption of the engine E, compared with the pour rate monitored via the mass flow sensor MFS, exceeds a preset limit at which operation of the harvester H is uneconomic and/or the chip quality deteriorates to an unacceptable level.

[0058] In addition to the state of the cutting edges 53 on the knives 50, the quality of the chips produced is also subject to other factors. In particular, the occurrence of chips with uneven surface can be due to excessive distance between anvil 60 and the knife-edges 53. It is important that as the knife-edges 53 wear, or are ground sharp, the anvil 60 is readjusted to the preferred path 54 for the cutting edges 53 of the knives 50.

[0059] Excessive anvil distance is created by not correctly setting the anvil up against the knife cutting radius. This phenomenon is also attributed to wood stems stacked on top of each other, as is normally found in standard disc- and drum- chippers, where the need to keep productivity rates high. Multi-stacked stems do not always have a solid anvil (or counter knife) to rest against, and therefore, can move unrestrained from the knife impacting the wood stem.

[0060] To ensure the anvil 60 is correctly set, an auto-adjustment system 90, to reset the distance of the anvil assembly 60, (and, in particular, the anvil plates 62) to the knife cutting edge path 54 , is provided, and will now be described with reference to FIGS 7 to 1 1 .

[0061 ] The auto-adjustment system 90 has a pair of spring steel strips 91 mounted at their proximal ends, by studs 92, adjacent the ends of the anvil head 61 , and the strips 91 extend a small distance past the anvil plates 62 towards the knife cutting path 54. A vibration sensor 93, e.g. an accelerometer, is mounted intermediate each strip 91 .

[0062] Referring to FIGS. 9 and 10, the vibration sensor 93 will determine when the anvil head 61 is located so that the knives 50 contact the distal ends of the strips 91 . When the knives 50 just contact the strips 91 , the correct spacing of e.g. 1 .0-1 .5mm between the anvil head 61 and the knife cutting radius path 54 is achieved. As illustrated in FIG. 9, the knife 50, moving in the direction of arrow K, will deflect the distal ends of the strips 91 (downwardly) in the direction of arrow S1 . When the knife 50 has passed the strip 91 , the distal end of the strip 91 will move (upwardly) in the direction of arrow S2 towards its original position. This movement, or vibration, of the strip will be detected by the vibration sensors 93, which will transmit signals indicating the relative location of the knives 50 from the anvil plates 62, and causing the anvil control ram 68 to cease movement of the shaft 72. If, however, if the distance between the knives 50 and the anvil plates 62 is reduced e.g. below 1 .Omm, the knives 50 will strike the strips 91 with greater force, thereby generating greater vibrations measured by the vibration sensors 93, the sensors 93 will transmit signals which will cause the anvil control ram 68 to pivot control lever 71 , and rotate control shaft 72, to move the anvil head 61 away from the knife cutting path 54 until the vibrations detected by the vibration sensors 93 are within acceptable limits.

[0063] The operational logic of both the sharpening system 10 and the auto-adjustment system 90 for the anvil assembly 60 will now be described, in the following chronological order, with reference to FIGS 1 1 and 12;:

1 . Operator depresses start button to engage CPU program

2. Sharpening clutch engages via C7

3. Sharpening motor spins drum via V5 (could be electric or hydraulic)

4. Position sensor indicates drum position and alignment of drum locating holes and lock off actuator via S6

5. Locking actuator extends dowel via C8 with position monitor via position sensor S8 to lock drum

6. Sharpening clutch disengages via C7

7. High pressure air cleaning (V9) engages

8. Main linear slide engages via C1 with the position monitored via S1 .

Transverses grinding head along full length of drum to take measurement.

9. Depth reading is taken by depth sensor via S3 (could be laser or contact roller)

10. Once knife edge surface depth is ascertained, grinding motor via V4 (electric or hydraulic) is engaged either by program control or manual setting.

1 1 . Linear cross slide traverses inwards via C2 with depth monitored by sensor S2.

12. Main linear slide engages via C1 with the position monitored via S1 . 13. CPU loops - main slide traverses full length, depth sensor records actual grinding depth via S3, cross slide increments in required amount (C2 & S2), main slide traverses again. High pressure air cleaning (V9) runs continuously through the loop to blow clean water and other contaminants that affect depth sensor function (S3).

14. When sufficient grinding depth is achieved (S3), cross slide retracts (C2 & S2), air is disabled (V9) and grinding motor is disabled (V4) and main linear slide moves grinding head to home position (C1 & S1 )

15. Locking actuator retracts dowel via C8 with position monitor via position sensor S8 to release drum

16. Step 2 repeats until all knives have been ground.

17. Sharpening clutch engages via C7

18. Sharpening motor spins drum via V5

19. Linear actuator on anvil and incrementally moves after each knife passes by until a vibration signature is detected by acceleration sensor on metal spring tag.

20. Linear actuator on anvil steps back a predetermined distance, until no contact is sensed after one complete revolution of the drum

21 . Sharpening motor turns off via V5

22. Sharpening clutch disengages via C7

23. Messages sent from CPU to operator monitor to advise on total amount ground, knife life left etc.

[0064] The above description is directed to a sharpening system 10 for chipping drums; but the system can be suitably modified for the sharpening of the knives of disc chippers. The sharpening system 1 10, of the second embodiment of the present invention, will now be described with reference to FIGS. 13 and 14. NB: Where possible identical, or closely related, features of the sharpening system 1 10 will be identified by reference numerals 1 xx, where xx is the reference numeral for the sharpening system 10. For example, disc chipper 140 has a (substantially vertical) axis of rotation 142; and knives 150 have cutting edges 153. [0065] The sharpening system 1 10 has a first carrier 1 1 1 and second carrier 120, and sharpening head 125 (with a sharpening stone 126) substantially as hereinbefore described. The sharpening head 125 is extended through a respective slot 148 in a top plate 144 of the disc chipper 140; and is moved by the second carrier 120 with a direction of motion substantially parallel to the shaft 141 (from which the knives 150 extend radially) and to the axis of rotation 142; and that the first carrier 1 15 guides the sharpening head 125 along the cutting edges 153 of the knives 150 in a direction substantially transverse (or radial) to the axis of rotation 142.

[0066] The alignment mechanism 180 locks the sharpening system 1 10 against relative rotation to the top plate 144 during the sharpening sequence for a particular knife 150.

[0067] The skilled addressee will readily appreciate that the present invention provides considerable advantages over the prior art knife or blade sharpeners described in the PRIOR ART discussion above.

[0068] The in-situ knife sharpening system of the present invention is designed to precisely locate the knife cutting edge geometry while traversing the spinning grinding stone along the drum (or knife) length and incrementally feeding it into the knife with each pass. This wet grinding process, simulates an optimal knife sharpening device, but without the need to remove the knives for each grinding event. This yields the following benefits:

1 . Facilitates more grinding events to occur before the knives or blades become too worn causing excessive energy consumption and denigration of wood chip quality;

2. The knife-edge radius is precisely maintained so each knife or blade is cutting at exactly the same cutting depth, so one knife or blade isn't subjected to greater cutting load and therefore there is no imbalance in wear between knives or blades; 3. A precise knife-edge radius also enables a precise gap to be maintained along the full length of the anvil. This is always disturbed when knives or blades are replaced each time; and.

4. Significantly reduces the total time spent changing the knives or blades over the life of the chipping drum or disc chipper.

[0069] The skilled addressee will appreciate that the sharpening system of the present invention provides other benefits over the PRIOR ART hereinbefore described; and that the above list of advantages is by way of examples only.

[0070] Various changes and modifications may be made to the preferred embodiments described and illustrated without departing from the scope of the present invention.

[0071 ] In this specification, the terms 'comprises', 'comprising', 'includes', 'including', or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.