FIELD OF THE INVENTION

The present invention pertains to a device for extracting a tree stump from the ground, which device utilizes an annular sawing means for detaching the tree stump from its roots. BACKGROUND OF THE INVENTION

In recent years, removing of tree stumps from the ground after felling has increased. In one aspect, the tree stump is a valuable resource since it comprises a large amount of fiber material, but the removal of tree stumps is also important to facilitate plantation of new trees and to decrease problems with root disease. Since fungal inoculums residing in roots and stumps after final felling can remain viable for decades, there is an increased risk of mortality in subsequently planted trees.

A device for extracting a tree stump from the ground according to the above is disclosed in SE524015C2, which shows a device which comprises an annular sawing means arranged in a cylinder portion enclosing an internal space. The sawing means is arranged for simultaneous rotation and advancement along its axis of rotation for detaching a tree stump from its roots in the ground. The device further comprises an expel means arranged inside the cylinder portion which, upon activation, in respect thereto is downwardly movably arranged for expelling the detached tree stump from the internal space. The known device for extracting tree stumps is generally advantageous in that it provides a fast en simple extraction of tree stumps from the ground without simultaneously extracting the typically extensive root system thereof. However, due to tough operation conditions the annular sawing means for the known device is a wearing part which requires frequent and time- consuming maintenance or replacement.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved device for extracting a tree stump from the ground. It would further be advantageous to achieve a device for extracting a tree stump from the ground with an improved life time expectancy of the sawing means. Preferred embodiments are set forth in the dependent claims and in the following description and drawings. The inventive concept of the device for extracting a tree stump from the ground of the present invention is based on an insight that by controlling the application of the sawing means into the ground, its life time expectancy increases and the detaching of the tree stumps becomes more efficient and stable.

Thus, in accordance with the present inventive concept, there is provided a device for extracting a tree stump from the ground, the device comprising: an annular sawing means for detaching the tree stump from its roots in the ground, which sawing means comprises a cylinder portion having an opening. The cylinder portion encloses an internal space for confining the tree stump, an expel means arranged inside the cylinder portion, which expel means in respect thereto is movably arranged, and a feeding advancement mechanism of the sawing means arranged to control the expel means to bear against the tree stump during detaching thereof.

The feeding advancement means according to the present invention is arranged for controlling a current vertical position of the sawing means along its axis of rotation by controlling the expel means, which in contrast to the known device above, is activated during detaching of the tree stump, and arranged to bear against the tree stump at substantially all times during detaching of the tree stump. This provides a more controlled operation of the sawing means as it provides stabilization during sawing.

According to an embodiment of the device, it comprises a sensor means for detecting a working condition of the device being one of a current contact pressure of the sawing means, a current contact pressure of the expel means, and a current rotation speed of said sawing means, which is advantageous e.g. to initially detect when the expel means actually bears against the tree stump, or to detect when the applied pressure load of the sawing means to the ground is too big. The sensor means may for instance be a hydraulic compression force sensor, any other applicable force sensor or pressure sensor, or a revolution counter.

According to an embodiment of the device, the feeding advancement mechanism is arranged to, based on the detected working condition control the expel means, obtain or preserve a predetermined working condition during detaching of the tree stump. For instance, as the sawing means is lowered over the tree stump and subsequently digs through the ground and the roots, the contact pressure between the expel means and the tree stump will increase. To preserve a preset/predetermined contact pressure value, the expel means is thus continuously adjusted to let the tree stump be further received inside the cylinder portion, which in turn lowers the vertical position of the sawing means and allows it to keep sawing further into the ground. Further, as the sawing means is lowered over the tree stump, either by its own weight or by an external pressure load being applied, e.g. by means of a drive mechanism or a crane carrying the stump extractor device, and subsequently digs through the ground and the roots, the contact pressure between the sawing means and the ground/tree roots can exceed or be less than a predetermined optimal contact pressure value. To preserve the predetermined contact pressure value, the expel means is controlled in response to detecting a current working condition of the sawing means, and in response thereto continuously adjust the expel means to let the tree stump be further received inside the cylinder portion or to push it outwards. This in turn controls the vertical position of the sawing means and thereby controls the contact pressure between of the sawing means.

According to an embodiment of the device, the feeding advancement mechanism is further arranged to control the expel means in response to the rotation speed of the sawing means. If the rotation speed decreases for instance due to high resistance in the ground (or by the contact pressure increasing on the sawing means as it is pushed into the ground), the expel means is adjusted to push the tree stump a short portion out of the cylinder portion, thereby raising the vertical position of the sawing means. As the sawing means is lifted, the rotation speed is allowed to increase to a predetermined rotation speed again. This is advantageous as the wear on the sawing means decreases, and the risk of the sawing means getting stuck decreases.

According to an embodiment of the device, the expel means comprises a stem and a supporting element. The supporting element is preferably a circular plate having a diameter close to an inner diameter of the cylinder portion, which is advantageous to stabilize the rotation of the sawing means. According to an embodiment of the device, the expel means comprises a centering element, which is advantageous to stabilize the rotation of the sawing means.

According to an embodiment of the device, the device further comprises a splitting element arranged for, when being in a first position, at least partly intersecting the opening, thereby providing splitting of the detached tree stump as it is expelled from the sawing means. This advantageously provides a more efficient handling of the extracted tree stump after extraction from the ground. By splitting the tree stump, remaining soil and stones are separated from the tree stump. Further, by splitting the tree stumps, the time for seasoning of the material decreases.

According to an embodiment of the device, the splitting element is arranged to be movable between at least the first position and a second position where it is distanced from the opening. The latter position allows for the sawing means to work freely and thereby facilitates detaching of the tree stump from the ground.

According to an embodiment of the device, the device further comprises a positioning mechanism for controlling the position of the splitting element.

According to an embodiment of the device, the positioning mechanism comprises a support element which is arranged to at least partly bear against the cylinder portion when the splitting element is arranged in the first position. The support element advantageously increases the stability of splitting means and the device as the tree stump is expelled and split.

According to an aspect of the invention, there is provided a method for controlling feeding advancement of a device for extracting a tree stump according to the invention from the ground, the method comprising controlling the expel means to bear against said tree stump during detaching of the tree stump. According to an embodiment of the method, it further comprises detecting a working condition of the device being one of a current contact pressure of the sawing means, a current contact pressure of the expel means, and a current rotation speed of the sawing means; and controlling a vertical position of the sawing means along its axis of rotation based on the detected working condition. According to an embodiment of the method, the step of controlling comprises adjusting a vertical position of the expel means. There is provided a second device for extracting a tree stump from the ground, the device comprising an annular sawing means for detaching the tree stump from its roots in the ground comprising a cylinder portion having an opening. The cylinder portion encloses an internal space for confining the tree stump, an expel means arranged inside the cylinder portion, and which in respect thereto is downwardly movably arranged for expelling the detached tree stump from the internal space, and a splitting element arranged for, when being in a first position, at least partly intersecting the opening, thereby providing splitting of the detached tree stump as it is expelled from the sawing means. This advantageously provides a more efficient handling of the extracted tree stump after extraction from the ground. By splitting the tree stump, remaining soil and stones are separated from the tree stump. Further, by splitting the tree stumps, the time for seasoning of the material decreases.

According to an embodiment of the second device, the splitting element is arranged to be movable between at least the first position, and a second position where it is distanced from the opening.

According to an embodiment, the second device further comprises a positioning mechanism for controlling the position of the splitting element.

According to an embodiment of the second device, the positioning mechanism comprises a support element which is arranged to at least partly bear against the cylinder portion when the splitting element is arranged in the first position.

According to an embodiment of the second device, the splitting element comprises at least one elongated knife blade or splitting wedge.

According to an embodiment of the second device, the splitting element is arranged to split the stump into more than two pieces. According to an embodiment of the second device, the splitting element is I-shaped, Y-shaped, or star shaped.

It is noted that the invention relates to all possible combinations of features recited in the claims. These and other aspects, features, and advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail and with reference to the appended drawings in which:

Fig. la) and b) are schematic illustrations showing a cut open cross sectional side view of an embodiment of a device according to the present invention; and

Fig. 2a) - 2c) are schematic illustrations showing different side views of an embodiment of a device according to the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings. The below embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

Fig. la) is a schematic illustration showing a partly cut open cross sectional side view of an embodiment of a device for extracting a tree stump from the ground according to the present invention, which for simplicity herein after is referred to as "stump extractor device". The shown stump extractor device 100 comprises a sawing means 110 comprising a hollow cylinder 1 15 which has an open end 116, and which encloses a space 117. The cylinder 115 is adapted to rotate about its central axis x - x. The cylinder 115 is rotatably arranged with respect to a support structure 140, here by means of a slewing bearing. A drive mechanism for the sawing means, here a hydraulic drive mechanism, is arranged inside the support structure 140 (not shown). Further, a connection element 150 is arranged on the supporting structure 140 to which a sub frame of e.g. a crane of a suitable carrier vehicle, like for instance an excavator, or a forest machine is connected when the stump extractor device 100 is used (not shown). The lower rim 118 at the open end 116 of the cylinder 115 is arranged having serrations, cutters, a toothing or similar.

Detaching of a tree stump is done by lowering the cylinder 115 over the tree stump while the sawing means 110 is activated. The cylinder 115 is preferably oriented such that its central axis x-x, and a central axis of the tree stump substantially coincide. When reaching ground, the sawing means 110, i.e. lower rim 118, cuts through the dirt in the ground and through roots of the tree stump and thereby detaches the tree stump. After detaching of the tree stump, the sawing means 110 is then lifted by means of the crane, and due to remaining portions of the roots or buttresses of the stump core and dirt etc. putting pressure towards the inner side of the cylinder 115, the detached stump core remains inside the cylinder 115 during the lift.

To continue with reference to Fig. la), as mentioned above, the stump extractor device 100 further comprises expel means 130 for expelling the detached tree stump from the sawing means 110. In the exemplifying embodiment the expel means 130 comprises a plate 132 carried by a lower end of a stem 133. The plate 132 is perpendicularly oriented with respect to the stem 133. The stem 133 is here a piston rod coupled to a double-acting hydraulic cylinder system, which is arranged inside and fixated to the supporting structure 140. A cylinder element 134, in which a piston connected to the piston rod moves back and forth upon activation, is arranged inside the supporting structure 140, while the piston rod, i.e. stem 133, which is coupled to the cylinder element 134, operates within the space 117 of the sawing means 110. The stem 133 is arranged such that its operation coincides with the central axis x-x of the cylinder 115. In Fig. la), the stem 133, and thereby the expel means 130, is fully expelled from the supporting structure 140. In Fig. lb), the expel means 130 is shown when the stem 133 is retracted into the cylinder element 134, which will be the case when a tree stump is present inside the cylinder 115. The expel means 130 is utilized to after detaching of the tree stump, i.e. when a tree stump has been lifted from the ground and is confined inside the cylinder 115, expel the tree stump from the sawing means 110. That is, the stem 133 is then operated to push out the tree stump from the cylinder 115.

Returning now to the start of the operation to detach the tree stump from the ground, the expel means 130 is initially in its fully expelled position as illustrated in Fig. la) such that when the cylinder 115 is lowered from above over the tree stump, the plate 132 bears against the top of the tree stump.

According to an embodiment of the stump extractor device, it comprises a sensor means for detecting a working condition of the stump extractor device, and a feeding advancement mechanism arranged for controlling a current vertical position of the sawing means along its axis of rotation based on the detected working condition. During detaching of tree stump, the hydraulic cylinder system is actuated, e.g. by means of a hydraulic drive system, and the stem 133 is pushed along the central axis x-x of the cylinder 115 pushing the plate 132 towards the tree stump present at the open end 16 or being at least partly inside the space 117, such that the plate 132 and an optional pin element 131 is pressed with a predetermined contact pressure against the tree stump. This advantageously stabilizes the rotary operation of the sawing means 110.

According to an embodiment of the stump extractor device, sensor means, here a hydraulic compression force sensor of the hydraulic drive system, is utilized to detect a current working condition of the stump retractor device. The pressure in the hydraulic drive system, which drives the sawing means, indicates the current working load acting on the sawing means, corresponding to the contact pressure on the sawing means. A high hydraulic pressure indicates a heavy working load (a heavy working condition of the sawing means), and vice versa. Further, the current vertical position of the sawing means 110 along its axis of rotation during detaching of the tree stump is controlled in response to the detected working condition. As the sawing means 110 is pushed down over the tree stump, the expel means 130 is controlled to maintain a predetermined working condition, e.g. the contact pressure of the sawing means and the tree stump or the speed of rotation of the sawing means, by retracting or expelling the stem 133 to allow the tree stump to enter or to be pushed outwardly from the cylinder 115, thereby providing lowering or raising of the sawing means over the tree stump, in a controlled manner.

According to an embodiment of the stump extractor device, the control of the expel means, and thereby the current vertical position of the sawing means, is further done in response to a current rotation speed of the sawing means. If the rotation speed of the sawing means decreases below a given threshold value or, e.g. because the cylinder is lowered to quickly or if the ground is very hard, the expel means are pushed out to lift the sawing means from the ground/roots to maintain a predetermined rotation speed.

According to the exemplifying embodiment of the stump extractor device, the support element of the expel means, cf. plate 132 above, is provided with a centering element, here in the form of a pin element 131 (optional) which is pressed into the top of tree stump during sawing thereby facilitating for the sawing means to run true. The diameter of the plate 132 is preferably selected to be close to, but less than, an inner diameter of the cylinder 115. The inner surface of the cylinder is according to an embodiment of the device provided with flat distance elements (not shown) arranged circumferentially to the plate 132 and evenly distributed about the inner surface, to provide a distance between the rotating sawing means 110 and the plate 132 during operation.

According to embodiments of the stump extractor device, the free end of the expel means, the end of stem 133, is arranged with no plate or with some other applicable support element, other than the shown plate 132.

The diameter of the cylinder 115 is typically adapted to the size of the tree stumps to be extracted from the ground. When extracting stumps from small saw timber, a cylinder diameter of at least 20 - 40 cm is applicable. For extraction of stumps from large diameter logs a cylinder diameter of about 80 -100 cm (or more) is applicable.

According to an embodiment of the stump extractor device, the diameter of the cylinder 115 is selected to be less than the tree stump diameter, thereby providing a cylinder shaped stump core, i.e. a stump core without any buttresses.

To continue now with reference to Fig. 2a), there is provided a stump extractor device 200 with a similar structure as described above with reference to Fig. 1, i.e. which comprises a sawing means 110 comprising a hollow cylinder 115 which has an open end, opening 116, and which encloses a space 117. The cylinder 115 is adapted to rotate about its central axis x - x. The cylinder 115 is rotatably arranged with respect to a support structure 140. The stump extractor device 200 further comprises a splitting means 160 arranged for splitting the detached tree stump as it is expelled from the cylinder 115. In the exemplifying embodiment 200, the splitting means comprises a splitting element in the form of a knife blade 161, which is connected to a positioning mechanism 162 which enables the knife blade 161 to be folded between a first position, and a second position. In the first position, the knife 161 is positioned vertically below the opening 116 of the cylinder 115, as is shown in Fig. 2a. The splitting element is positioned in the first position such that the knife 161 is oriented with an edge 161b thereof facing the opening 116 of the cylinder 115. When the detached tree stump is expelled/pushed out from the cylinder 115 by means of the expel means 130, as previously described, the knife blade 161 splits it into two pieces. The knife 161 is here positioned at a center of the open end 116, and thereby intersects the central axis x-x- of the stump extractor device 100. Such positioning of the knife substantially provides splitting of the stump in two more or less equally large pieces.

In the second position, the knife 161 is positioned distanced from the opening 116 of the cylinder 115. In Fig. 2b) the positioning mechanism 162 provides a second position, substantially above and at a side (right-hand in the figure) of the cylinder 115, which leaves the cylinder 115 and thereby the sawing means free, such that it can be operated into the ground during detaching of the tree stump.

The positioning mechanism 162 here comprises a rotatable axis 173 (visible in Fig. 2c)) onto which the splitting means knife 161, is engaged. The rotatable axis 173 is on its respective end portions connected via a respective linkage 174 to a bracket 163. The bracket 163 and the splitting means are arranged on opposite sides of the cylinder 115. Each linkage 174 comprises a lower lever 164, and a linked upper lever 165. The lower lever 164 is at a first end portion thereof pivotally engaged with the rotatable axis 173, and on a second opposite end portion thereof pivotally arranged with the bracket 163. The upper lever 165 is at a first end portion thereof pivotally engaged with the rotatable axis 173, and, via a pivotally arranged link 165b on a second opposite end portion thereof, pivotally arranged with the bracket 163. Further, at each end portion of the rotatable axis 173, it is connected to a respective piston rod 169a coupled to a double-acting hydraulic cylinder system 169 which at its opposite end is fixated to the support structure 140. As the cylinder system 169 is actuated, the rod piston rod 169a, is movable between being fully expelled with reference to the supporting structure 140, as shown in Fig. 2a) which causes the linkage 174 to be lowered, thereby placing the splitting element in its first position.

According to an embodiment of the stump extractor device, the bracket 163 is arranged to, when the splitting means is arranged in its first position, bear against the cylinder 115 thereby providing an extra support during the splitting of the tree stump, and to in the second position, as illustrated in Fig. 2b) to be separated from the cylinder 115 by a predetermined distance Δχ to allow the sawing means 110 to rotate freely. In the exemplifying embodiment, the distance Δχ is provided by means of a loose or a play in a bracket engagement 163b with the support structure 140 which allows a lower portion of the bracket 163 to act as a support element for the splitting means.

According to an embodiment of the stump extractor device, the splitting means comprises at least one elongated knife blade or splitting wedge, which splits the detached tree stump. In an alternative embodiment, the splitting means is arranged to split the stump into more than two pieces. For instance a Y-shaped splitting element, with three knife blades extending from a common centre, provides tree pieces of the stump. With even more knife blades extending from the common centre, forming a star shaped splitting element, a greater number of pieces can be produced, as long as the expel means can provide a high enough force to push the tree stump through the splitting means.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. For instance, the drive mechanism for the sawing means and the expel means may comprise electrical motors and/or control elements, the positioning means of the splitting means may be arranged in alternative manners, a control system, the feeding advancement mechanism, which in the exemplifying example is provided within the hydraulic drive mechanism, to control the sawing means and the expel means can be based on some other applicable logic control system e.g. by means of a Programmable Logic Control (PLC) device etc. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. Any reference signs in the claims should not be construed as limiting the scope.